(WIP) Define ResultSpec and ListResult

TODO:
* doc popping filters
Remove GetParamsCheckMixin and ControlParamsCheckMixin
Change signature for data.get to take a ResultSpec, and no options

This also changes the endpoint test method callGet to take a path rather
than kwargs.

TODO:
* doc sig changes
* doc get resultspec args
(WIP) indicate whether an endpoint returns a collection

..and the plural form of a ResourceType

TODO: docs
(WIP) add support for query args in links

TODO:
 * doc
factor out string-to-boolean operations
(WIP) add getEndpoint method

TODO:
* tests
* docs
WIP - rest + jsonrpc