Extend inline / fixed length bytes array support (issue #244)

Extend inline / fixed length bytes array support (issue #244)

Adds support for proto3 and POINTER field types to have
fixed length bytes arrays. Also changed the .proto option
to a separate fixed_length:true, while also supporting the old FT_INLINE
option.

Restructured the generator and decoder logic to threat the inline
bytes fields more like "just another field type".