Refactored functions creation

[KOLANICH]

performance issues from #12 should be solved now (use dis.dis(kaitaistruct.KaitaiStream.read_s4be) to understand why).

[GreyCat]

This is unlikely to be accepted either:

• This still replaces simple and straightforward code with complex and harder-to-understand one. Basically any code metric (i.e. cyclomatic complexity, maintainability score, etc) indicates that it's more complex that it was.
• This brings extra dependency.
• You still haven't provided by benchmarks that support performance claims.
• Meta-programming machinery still potentially generates problems with using this code with Cython, Python-into-something transpilers, etc, etc.

[KOLANICH]

I have done some benchmarking, it is really slower. Strangely, after using bind it has became even slower (for now I don't know why, on synthetic tests bind gives speed-up, and the byte-code of optimized functions is identical to the original ones).