Add and use Database.open as a wrapper around notmuch.Database()
Use one afew.Database.Database object for all filters
Add Database.close
Flush all internal structures at the end of Filter.commit()
Add functions to add and remove mails from the index
Use a shorter default retry delay, write fewer log messages
Fix three pyflakes warnings
Add the ability to use inotify to watch for new mails
Integrate the ability to watch for new mails into afew