io.encodings.utf7: implementation of decoding for new codec utf7
io.encodings.utf7: better encoding using the group-by combinator
io.encodings.utf7: decoder implementation, doesn't support utf7imap4 yet
io.encodings.utf7: working utf7 decoding with tests
io.encodings.utf7: documentation and metadata files
io.encodings.utf7: cleaned up vocab per review

1. Tuple is used to hold the decoding buffer instead of a global
2. Fixed problematic sequence type conversions.