Split ERC20Votes and ERC20VotesComp

[Amxx]

ERC20Votes include:

function delegates(address owner) external view returns (address);
function checkpoints(address account, uint32 pos) external view returns (Checkpoint memory);
function numCheckpoints(address account) external view returns (uint32);
function getVotes(address account) external view returns (uint256);
function getPastVotes(address account, uint256 blockNumber) external view returns (uint256);
function getPastTotalSupply(uint256 blockNumber) external view returns(uint256);
function delegate(address delegatee) external;
function delegateBySig(address delegatee, uint nonce, uint expiry, uint8 v, bytes32 r, bytes32 s) external;

ERC20VotesComp include all the the above plus:

function getCurrentVotes(address account) external view returns (uint96);
function getPriorVotes(address account, uint256 blockNumber) external view returns (uint96);

ERC20VotesComp will also override the total supply cap from 2224 (as in ERC20Votes) to 296

PR Checklist

• Tests
• Documentation
• Changelog entry

[frangio]

I made a few changes, everything else looks good!