Always use URI Templates

Switching over to URI Templates is one of the major objectives on the roadmap. URI templates make a lot of interesting features easier, especially for simulating consumers, and fits with a lot of documentation formats that are starting to shift to URI templates.

The only thing I'm not 100% sure about is if we should drop regex support completely, or just prefer URI templates to regex. I'm leaning towards dropping it for simplicity and seeing if any situations come up where a URI template isn't usable.