Update docs for ALPM::DB and ALPM::DB::Sync.

Typoes were fixed in ALPM::DBs docs.
Fix typos in doc. No get_ prefixes the localdb method.

I removed the get_ prefix from get_localdb and get_syncdbs. Even though
they are options, there is no equivalent set_localdb or set_syncdbs. For this
reason these methods do not seem to fit with the other option mutators
and accessors.
Rewrite the docs for ALPM::Package.