Fix the CC expiration in tests

Tests were failing because it is now 2013. This change is safe for another
eight years.
Add support for getting customers

This is useful, for when you don't store any user info other than their
stripe customer id.
Make optional fields optional when creating a user

This enables the use-case where a customer is created when a user signs up,
but doesn't give any useful billing information. That way a trial can be
started, and later the user can add billing information without loosing or
restarting the trial
Add Quantity to subscription update
Add a bunch of missing fields from #stripe_customer

This change adds a bunch fields (in particular the subscription field) to
the stripe_customer record.
Reconcile Stefan changes with my unpushed commits

Bad matt.  Push your changes!

For these merge conflicts, Stefan's changes override
my own.  The only change I made to Stefan's commits
is 'deleted' to 'delete' in request_run/3.

Conflicts:
	include/stripe.hrl
	src/stripe.erl
Bump to version 0.5.0

Note: record definitions change in this version.
You need to recompile all modules including stripe.hrl.

All 7 tests pass.
Update README description and code snippet