lib,test: replace connection query() method with sync_exec{,_params}. The old generic name was deprecated in favor of the explicit synchronous with/without-params methods.
lib: replace two PG::Connection.connect with PG::Connection.new.
Wrap all close() calls in "ensure" blocks and simplify DB connection-making.
Document everything with YARD and fix some bugs along the way.
Stop pretending that we'll ever work with another DBMS.
Overhaul everything to get consistent error reports.
Replace 'account' with 'user' everywhere.
Rename PostfixadminDb, RoundcubeDb without the Db suffix. Make PostfixadminDb a regular plugin.