Add post-processing reminder for formats output

formats aren't stored with cards, should be calculated if they're
one of the requested fields
Test flask-restful reqparse module

I'll eventually be using this for parsing the search string and
various options (fields, dupes)
Rename returned fields for clarity

cost, name, power, toughness added a printed_ prefix to make it clear
that these are the raw values from the card, and as such aren't
necessarily sortable (due to stuff like {2/g} and HalfW).

This also means the same field names used in searching correspond
to returned values.
Overhaul README with first draft API

Added inital descriptions of the search API.  It still feels a bit
rough around the edges, I'll hopefully clean that up as I work through
the implementation.  Notably lacking details about error messages.