LibMath - Inaccurate declaration of _UINT256_MAX
`LibMathUnsigned` declares `_UINT256_MAX` as `2^255-1` while this value actually represents `_INT256_MAX`. This appears to just be a naming issue.\\n(UINT256_MAX/2-1 => pos INT256_MAX; 2**256/2-1==2**255-1)\\n```\\nlibrary LibMathUnsigned {\\n    uint256 private constant \\_WAD = 10\\*\\*18;\\n    uint256 private constant \\_UINT256\\_MAX = 2\\*\\*255 - 1;\\n```\\n
Rename `_UINT256_MAX` to `_INT256MAX` or `_SIGNED_INT256MAX`.
```\\nlibrary LibMathUnsigned {\\n    uint256 private constant \\_WAD = 10\\*\\*18;\\n    uint256 private constant \\_UINT256\\_MAX = 2\\*\\*255 - 1;\\n```\\n