Add [append_uidplus]
Parse UID's as non-zero ints
Connection mechanism moved to Imap_io_low
Fix interface of UIDPLUS, CONDSTORE commands
Make [Imap_parser.nstring] return option type
Add [Imap.connect_simple]
[Imap_set.singleton] -> [Imap_set.single], add [Imap_set.single']
Update README
Fix debug switch
Fix test
Fix to work with latest ocaml-gsasl