Create API for use by other applications.

[TheCDC]

I've been using Card Codex since the first Reddit post advertising its existence and figure it was time to give back.

This change exposes the context object previously only used to in rendering templates at the /api/ url.

For example, /api/?card=River%20Hoopoe returns a JSON response for the results of searching for River Hoopoe instead of rendered HTML. It also accepts the &page=N url parameter.