Restructure modules

[andrewthad]

Currently, bytebuild just dumps all kinds of encodings into a single module. By contrast, bytesmith breaks things up a little better:

Data.Bytes.Parser
    Data.Bytes.Parser.Ascii
    Data.Bytes.Parser.BigEndian
    Data.Bytes.Parser.Latin
    Data.Bytes.Parser.LittleEndian
    Data.Bytes.Parser.Unsafe
    Data.Bytes.Parser.Utf8

This nicest thing about this is that big-endian and little-endian encodings are almost never used together. There's less opportunity to make a mistake using the library when the combinators you don't want to use aren't in scope. It also helps avoid goofy suffixed names.