docs: Update external links to github repos that were moved

docs/contracts/events.rst

@@ -161,5 +161,5 @@ Additional Resources for Understanding Events
 ==============================================
 
 - `Javascript documentation <https://github.com/ethereum/web3.js/blob/1.x/docs/web3-eth-contract.rst#events>`_
-- `Example usage of events <https://github.com/debris/smart-exchange/blob/master/lib/contracts/SmartExchange.sol>`_
-- `How to access them in js <https://github.com/debris/smart-exchange/blob/master/lib/exchange_transactions.js>`_
+- `Example usage of events <https://github.com/ethchange/smart-exchange/blob/master/lib/contracts/SmartExchange.sol>`_
+- `How to access them in js <https://github.com/ethchange/smart-exchange/blob/master/lib/exchange_transactions.js>`_

docs/metadata.rst

@@ -202,6 +202,6 @@ This automatically verifies the metadata since its hash is part of the bytecode.
 Excess data corresponds to the constructor input data, which should be decoded
 according to the interface and presented to the user.
 
-In the repository `source-verify <https://github.com/ethereum/source-verify>`_
+In the repository `sourcify <https://github.com/ethereum/sourcify>`_
 (`npm package <https://www.npmjs.com/package/source-verify>`_) you can see
 example code that shows how to use this feature.

docs/resources.rst

@@ -75,7 +75,7 @@ Solidity Integrations
     * `Vim Solidity <https://github.com/tomlion/vim-solidity/>`_
         Plugin for the Vim editor providing syntax highlighting.
 
-    * `Vim Syntastic <https://github.com/scrooloose/syntastic>`_
+    * `Vim Syntastic <https://github.com/vim-syntastic/syntastic>`_
         Plugin for the Vim editor providing compile checking.
 
 * Visual Studio Code:
@@ -145,5 +145,5 @@ Third-Party Solidity Parsers and Grammars
 * `solidity-parser <https://github.com/ConsenSys/solidity-parser>`_
     Solidity parser for JavaScript
 
-* `Solidity Grammar for ANTLR 4 <https://github.com/federicobond/solidity-antlr4>`_
+* `Solidity Grammar for ANTLR 4 <https://github.com/solidityj/solidity-antlr4>`_
     Solidity grammar for the ANTLR 4 parser generator

docs/security-considerations.rst

@@ -259,7 +259,7 @@ more special edge cases for signed numbers.
 
 Try to use ``require`` to limit the size of inputs to a reasonable range and use the
 :ref:`SMT checker<smt_checker>` to find potential overflows, or use a library like
-`SafeMath <https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/contracts/math/SafeMath.sol>`_
+`SafeMath <https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/math/SafeMath.sol>`_
 if you want all overflows to cause a revert.
 
 Code such as ``require((balanceOf[_to] + _value) >= balanceOf[_to])`` can also help you check if values are what you expect.