Add byte decoder

[lcswillems]

Supports uint, biguint, string, boolean, tuple, list. With top-level & nested encoding.

In order to test the decoder, uncomment the commented lines at the end of utils/utils_decode.py and run:

python3 utils/utils_decode.py

This would decode 000000030c0d0e00000007626f6e6a6f7572000000010c using given decoder:

d.Tuple({
    "a": d.List(d.U8()),
    "b": d.Tuple({
        "a": d.Str(),
        "b": d.U(),
    })
})

And output will be:

{'a': [12, 13, 14], 'b': {'a': 'bonjour', 'b': 12}}