Related to #187, I'm opening this so we can discuss how to precompile templates.

The general idea is how do we take creating a Template instance out of the first-render load time. Ie, make this new disappear, taking all of this (163 lines of very slow code!) out of the first render.

I think we can manage to precompile these in a build step, making a file instantiate Templates with the correct TemplateStringsArray and already instantiated TemplateParts (with the correct indexes). We might need to expose the templateCache externally.