Use sqlite for saved_state

[rshipp]

Writing the config every time we update the state is messy. With #39, this becomes even worse, since when we write out the config from the internal dict, it's not guaranteed to be in the same order we read it in.

As a cleaner implementation, change to reading/writing config from a sqlite database instead.

Basic design proposal:

• Config support for a new general variable, state_file, relative or absolute path to sqlite db.
• State class with get(name) and save(name).
• SQLite db with a table with name, state columns.

[rshipp]

Closed by #45.