- CommitCandidate allow save phrase and user_freq in user db.
- bugfix: GetCandidates SQL query ORDER BY field fixed.
- bugfix: fix a memleak in on_handle_get_candidates()
- minor bugfix: fix variable name in meson.build

get_candidates() implemented naively.

no jian pin support, no auto correction, no ambiguity pinyin support, but here
is a good foundation to work on.