Fix links in documentation (#3387)

contracts/crosschain/amb/CrossChainEnabledAMB.sol

@@ -7,19 +7,20 @@ import "../CrossChainEnabled.sol";
 import "./LibAMB.sol";
 
 /**
- * @dev [AMB](https://docs.tokenbridge.net/amb-bridge/about-amb-bridge)
+ * @dev https://docs.tokenbridge.net/amb-bridge/about-amb-bridge[AMB]
  * specialization or the {CrossChainEnabled} abstraction.
  *
  * As of february 2020, AMB bridges are available between the following chains:
- * - [ETH <> xDai](https://docs.tokenbridge.net/eth-xdai-amb-bridge/about-the-eth-xdai-amb)
- * - [ETH <> qDai](https://docs.tokenbridge.net/eth-qdai-bridge/about-the-eth-qdai-amb)
- * - [ETH <> ETC](https://docs.tokenbridge.net/eth-etc-amb-bridge/about-the-eth-etc-amb)
- * - [ETH <> BSC](https://docs.tokenbridge.net/eth-bsc-amb/about-the-eth-bsc-amb)
- * - [ETH <> POA](https://docs.tokenbridge.net/eth-poa-amb-bridge/about-the-eth-poa-amb)
- * - [BSC <> xDai](https://docs.tokenbridge.net/bsc-xdai-amb/about-the-bsc-xdai-amb)
- * - [POA <> xDai](https://docs.tokenbridge.net/poa-xdai-amb/about-the-poa-xdai-amb)
- * - [Rinkeby <> xDai](https://docs.tokenbridge.net/rinkeby-xdai-amb-bridge/about-the-rinkeby-xdai-amb)
- * - [Kovan <> Sokol](https://docs.tokenbridge.net/kovan-sokol-amb-bridge/about-the-kovan-sokol-amb)
+ *
+ * - https://docs.tokenbridge.net/eth-xdai-amb-bridge/about-the-eth-xdai-amb[ETH <> xDai]
+ * - https://docs.tokenbridge.net/eth-qdai-bridge/about-the-eth-qdai-amb[ETH <> qDai]
+ * - https://docs.tokenbridge.net/eth-etc-amb-bridge/about-the-eth-etc-amb[ETH <> ETC]
+ * - https://docs.tokenbridge.net/eth-bsc-amb/about-the-eth-bsc-amb[ETH <> BSC]
+ * - https://docs.tokenbridge.net/eth-poa-amb-bridge/about-the-eth-poa-amb[ETH <> POA]
+ * - https://docs.tokenbridge.net/bsc-xdai-amb/about-the-bsc-xdai-amb[BSC <> xDai]
+ * - https://docs.tokenbridge.net/poa-xdai-amb/about-the-poa-xdai-amb[POA <> xDai]
+ * - https://docs.tokenbridge.net/rinkeby-xdai-amb-bridge/about-the-rinkeby-xdai-amb[Rinkeby <> xDai]
+ * - https://docs.tokenbridge.net/kovan-sokol-amb-bridge/about-the-kovan-sokol-amb[Kovan <> Sokol]
  *
  * _Available since v4.6._
  */

contracts/crosschain/amb/LibAMB.sol

@@ -8,7 +8,7 @@ import "../errors.sol";
 
 /**
  * @dev Primitives for cross-chain aware contracts using the
- * [AMB](https://docs.tokenbridge.net/amb-bridge/about-amb-bridge)
+ * https://docs.tokenbridge.net/amb-bridge/about-amb-bridge[AMB]
  * family of bridges.
  */
 library LibAMB {

contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL1.sol

@@ -7,7 +7,7 @@ import "../CrossChainEnabled.sol";
 import "./LibArbitrumL1.sol";
 
 /**
- * @dev [Arbitrum](https://arbitrum.io/) specialization or the
+ * @dev https://arbitrum.io/[Arbitrum] specialization or the
  * {CrossChainEnabled} abstraction the L1 side (mainnet).
  *
  * This version should only be deployed on L1 to process cross-chain messages
@@ -15,7 +15,7 @@ import "./LibArbitrumL1.sol";
  *
  * The bridge contract is provided and maintained by the arbitrum team. You can
  * find the address of this contract on the rinkeby testnet in
- * [Arbitrum's developer documentation](https://developer.offchainlabs.com/docs/useful_addresses).
+ * https://developer.offchainlabs.com/docs/useful_addresses[Arbitrum's developer documentation].
  *
  * _Available since v4.6._
  */

contracts/crosschain/arbitrum/CrossChainEnabledArbitrumL2.sol

@@ -7,7 +7,7 @@ import "../CrossChainEnabled.sol";
 import "./LibArbitrumL2.sol";
 
 /**
- * @dev [Arbitrum](https://arbitrum.io/) specialization or the
+ * @dev https://arbitrum.io/[Arbitrum] specialization or the
  * {CrossChainEnabled} abstraction the L2 side (arbitrum).
  *
  * This version should only be deployed on L2 to process cross-chain messages

contracts/crosschain/arbitrum/LibArbitrumL1.sol

@@ -10,7 +10,7 @@ import "../errors.sol";
 
 /**
  * @dev Primitives for cross-chain aware contracts for
- * [Arbitrum](https://arbitrum.io/).
+ * https://arbitrum.io/[Arbitrum].
  *
  * This version should only be used on L1 to process cross-chain messages
  * originating from L2. For the other side, use {LibArbitrumL2}.

contracts/crosschain/arbitrum/LibArbitrumL2.sol

@@ -8,7 +8,7 @@ import "../errors.sol";
 
 /**
  * @dev Primitives for cross-chain aware contracts for
- * [Arbitrum](https://arbitrum.io/).
+ * https://arbitrum.io/[Arbitrum].
  *
  * This version should only be used on L2 to process cross-chain messages
  * originating from L1. For the other side, use {LibArbitrumL1}.

contracts/crosschain/optimism/CrossChainEnabledOptimism.sol

@@ -7,12 +7,12 @@ import "../CrossChainEnabled.sol";
 import "./LibOptimism.sol";
 
 /**
- * @dev [Optimism](https://www.optimism.io/) specialization or the
+ * @dev https://www.optimism.io/[Optimism] specialization or the
  * {CrossChainEnabled} abstraction.
  *
  * The messenger (`CrossDomainMessenger`) contract is provided and maintained by
  * the optimism team. You can find the address of this contract on mainnet and
- * kovan in the [deployments section of Optimism monorepo](https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts/deployments).
+ * kovan in the https://github.com/ethereum-optimism/optimism/tree/develop/packages/contracts/deployments[deployments section of Optimism monorepo].
  *
  * _Available since v4.6._
  */

contracts/crosschain/optimism/LibOptimism.sol

@@ -7,8 +7,8 @@ import {ICrossDomainMessenger as Optimism_Bridge} from "../../vendor/optimism/IC
 import "../errors.sol";
 
 /**
- * @dev Primitives for cross-chain aware contracts for [Optimism](https://www.optimism.io/).
- * See the [documentation](https://community.optimism.io/docs/developers/bridge/messaging/#accessing-msg-sender)
+ * @dev Primitives for cross-chain aware contracts for https://www.optimism.io/[Optimism].
+ * See the https://community.optimism.io/docs/developers/bridge/messaging/#accessing-msg-sender[documentation]
  * for the functionality used here.
  */
 library LibOptimism {

contracts/crosschain/polygon/CrossChainEnabledPolygonChild.sol

@@ -11,7 +11,7 @@ import "../../vendor/polygon/IFxMessageProcessor.sol";
 address constant DEFAULT_SENDER = 0x000000000000000000000000000000000000dEaD;
 
 /**
- * @dev [Polygon](https://polygon.technology/) specialization or the
+ * @dev https://polygon.technology/[Polygon] specialization or the
  * {CrossChainEnabled} abstraction the child side (polygon/mumbai).
  *
  * This version should only be deployed on child chain to process cross-chain
@@ -19,7 +19,7 @@ address constant DEFAULT_SENDER = 0x000000000000000000000000000000000000dEaD;
  *
  * The fxChild contract is provided and maintained by the polygon team. You can
  * find the address of this contract polygon and mumbai in
- * [Polygon's Fx-Portal documentation](https://docs.polygon.technology/docs/develop/l1-l2-communication/fx-portal/#contract-addresses).
+ * https://docs.polygon.technology/docs/develop/l1-l2-communication/fx-portal/#contract-addresses[Polygon's Fx-Portal documentation].
  *
  * _Available since v4.6._
  */