Only calcsize() and unpack() functions provided so far, for little-endian
byte order. Format strings don't support repition spec (like "2b3i").

Unfortunately, dealing with all the various binary type sizes and alignments
will lead to quite a bloated "binary" helper functions  - if optimizing for
speed. Need to think if using dynamic parametrized algos makes more sense.

Remove unnecessary includes. Add includes that improve portability.

Some functionality is still missing (eg and, or, bit shift), and some
things are buggy (eg subtract).

Done by introducing another factored out helper API in binary.c. This API
can be reused also by array and struct modules.