[FEATURE]: Add default settings support for tempy

[noprobelm]

Relates to #6

tempy should support the ability to specify default settings (i.e. location and system of measurement).

I'd like to use tempyrc for this. Right now, the Config class checks tempyrc for a user-provided API key. We'll need to expand the logic in the Config class to parse out each config option.

I suppose we should also add command line options for tempy to automatically update the config so the user doesn't have to go into tempyrc each time they want to make an update.