! Rename `EMPTY` to `MATCH` and `NOTHING` to `MISMATCH`
+ Add `asCharMask` to `CharPredicate`
+ Add `sliceCharArray` to `ParserInput`
! Change `MISMATCH` type from `Rule0` to `Rule[I, O]`
= Improve `run(<rule expr>)` and `~> (<rule expr>)` to also support `if` and `match`
+ Add `Base64Parsing` helper trait