Allow `--location` or `--latlon` arguments to fetch forecast.

The new `--location` option takes a human-readable location and attempts
to geocode it using the Google geocoding API.

Also included in this commit are some improvements to error and edge
case handling.
Allow a (clunky) way to provide a human-readable location.

Using that option requires changing the command in `index.coffee`. We
can internalize location auto-detection and make it more configurable;
all config options would go in `weather.conf` and the command would be
static.
Merge pull request #7 from tupton/3-human-readable-locations

Human-readable locations