Pull v1.1 out of the api_url and create a new method resources_url

I like the ability to get the url based on a token for the object type, but linked object's URLs from the responses already contain the v1.1 so if it's in the api_base, we can't use Clever.request to resolve link uris properly.
Implement a links method for Clever ApiResources
Implement District#schools that uses the links method.

This should be generalized to the other resources linked from District, but should NOT be generalized to link all resources to all other resources since the intended use for the data hierarchy is to request everything through a district.
Added methods to districts to get associated resources and support passing filters
Drop ruby 1.8.7 support
Merge pull request #6 from thinkthroughmath/linked_resources_from_district

Linked resources from district