wav: Rest of file should description not symbolic value
bencode: Remove redundant torepr example
mpeg_ps_packet,id3v1: Remove whitespace in symbolic value
Move scalar into own package.
Split scalar code into decode related scalar code (that reads etc) and
scalar code that just transform the scalar value.
Use a scalar.Mapper interface instead of just a function.
Make mappers, assert and validat impement the interface.