Make '.seen' persistent

Instead of using a dict, use a shelve so that seen is persistent across phenny
reloads.

This will cause some more disk IO as we are syncing the shelve every time
someone says something. It is probably better to just .close() the shelve when
phenny exits (using atexit).

Also, clean up some dead code that was left in the module.
Merge pull request #46 from rmoore/master

Make .seen persistent.
fix filename of seen.db files
add new metar parser and update weather module
switch tfw module to use new metar parser
fix test cases (wa changed something)
icao: remove EDDI (closed Berlin-Tempelhof airport)
fix inHg -> hPa conversion
add foodforus module
disable foodforus by default
foodforus: display errors
fix Wadsworth's Constant edge case and add test
fix immediate ping timeout on quakenet

https://github.com/sbp/phenny/pull/27
add unit tests for remind module
add .at command (need unit test)
foodforus: move api_key to end of signature
probably breaks stuff
Merge remote branch 'upstream/master'

Conflicts:
	modules/seen.py