Stripe Connect and Stripe.js customer token support

This pull request adds two new features:
- __Stripe Connect support.__ It uses http-conduit. Here are a few future changes to be made:
   - Unify the Stripe API and Stripe Connect http-conduit usage. Both use http-conduit but from different functions. b7adf61
   - The `client_id` for Stripe Connect should be added to the stripe config object. 3c51167
- Support for adding and updating __Customer objects with a Stripe.js token__. This fixes issue michaelschade/hs-stripe#4

Out of the 8 commits of mine included in this pull request, 6 are cleanups and improvements to Max's "library update patch": michaelschade/hs-stripe#5 which seems to work nicely based on my limited testing.

Happy Holidays!
-Luke