Document Crepe::API

Crepe is sorely lacking in documentation right now. This is a start, but
we'll need to tackle Endpoint and make the README much better soon.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Update bundle

I've considered removing Gemfile.lock entirely (as it's considered a
"best practice"), but I do find it helpful to include a specific
environment that is "known" to work.

Signed-off-by: Stephen Celis <stephen@stephencelis.com>