Rename struct for similarity in RFC-RAW

Renamed Decoder_aligned_res in Decoder_written

It's really the same, just that the RFC forces the
sizes of the memebers, while in the RAW API we can
keep size_t

also: bump up to 1.0.0-alpha1, things are much better
and consistent now

Signed-off-by: Luca Fulchir <luker@fenrirproject.org>