When using fetch, check and set cache as well.

Previously, using .get() on a resource would use the cache, but .fetch() would
never do so. This improves common workflows where one may store just the
resource id in a database as a reference and building the resource up from that
single piece of data.

Update version, changelog.
Merge branch 'master' of github.com:gadventures/gapipy

Conflicts:
	HISTORY.rst
Update version.