[uint] const matching doesn't work anymore

[ordian]

Apparently, in order to match on a const value, PartialEq and Eq must be derived:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=c371a6f8796511d84a21186cbb4ea352

So #390 was a breaking change that broke some code (Conflux-Chain/conflux-rust#1744, https://github.com/openethereum/openethereum/issues/11851).

As a quickfix we can revert this change and release a new version.