Adding parameter replacement

Provides token replacement for attribute routing template using a syntax like:

`api/[controller]/{id?}`

With this change the use of controller and action as parameters in attribute routes is disallowed, and will reported as an error. This is the cool new way to do it, which will provide more consistent behavior, and better performance.

Majority of the changes here are to provide a good experience for reporting errors across all the attribute routes.
@Eilon what about a nullable char? the appeal of using a single value to reflect the state is that the order of 'if/elseif/ doesn't matter. If `c` is `\0` then it's definitely not `[`, etc...