Changes:
* default value when no args
* license
* removed libc printing
* use extra::bigint instead of handmade gmp binding

The drawback is that it's 2 order of magnitude slower, the good news is that there is a good bench for extra::bigint.

Ignore more type aliases in unnecessary_cast

Fixes rust-lang#10555

changelog: [`unnecessary_cast`]: No longer lints cast from locals that are type aliases

Ignore more type aliases in `unnecessary_cast`

This is potentially the worst code I've ever written, and even if not, it's very close to being on par with starb. This will ignore `call() as i32` and `local_obtained_from_call as i32` now.

This should fix every reasonable way to reproduce rust-lang#10555, but likely not entirely.

changelog: Ignore more type aliases in `unnecessary_cast`