[maybe?] Create a common set of tags to aid in template compatibility between renderers

Currently, each renderer has its own completely separate set of tags. Thus, a given input string is tightly coupled to the formats/tags/parameters available on its own parser/renderer, and there's really no guarantee that any given string will be able to be used across multiple renderers.

There should be some way to enforce a common API across a minimal set of tags (such as `{{foreground}}`) so that there exists at lease _some_ compatibility across renderers. Having at least some tags that will always be able to be used from purely common code will help make it more intuitive, and avoid having to duplicating input strings to match the paramters/tag names available for a given renderer.