Add javascript-route-matcher package to dependencies
Begin implementing structured route generation

This begins to break Path generation into four parts:

1. A template representing the structure of the desired endpoint
   (_path.template)
2. A set of validators to enforce particular types of parameter
   within that template (_path.validators)
3. A data object containing values that will be mapped to endpoint
   template placeholders (_path.values)
4. A function to validate and render the path string (_pathStr)

TODO:

- Move the path generation and validation logic up into WPRequest
- Identify whether there's a cleaner way to do validation
- Improve tests and documentation
- Deprecate the _action/_actionId properties in favor of _path.values
- Implement the new behavior in all endpoints

Note: Removed route-matcher in favor of route-parser, which has a
more reliable route reversal method (i.e. stringifier).
Move path generation into WPRequest and change method names

PostsRequest URI generation is now handled within WPRequest, which
builds a path based on the _path.template string on the request
instance. Definition of the path structure and validators should
happen on the endpoint handler level; putting those together into a
final URL should be generic (and therefore live in WPRequest).

Identifiers changed:

* ._action, ._id, and ._actionId are now grouped in ._path.values
* .generateRequestUri() becomes ._renderURI()
* ._pathStr() becomes ._renderPath
Give WPRequest its own _path object with an empty template

This removes the need to do some conditional checks when rendering
Rename _queryStr to _renderQuery for consistency with _renderPath
Update doc blocks to correctly specify privacy
Implement new path construction within TaxonomiesRequest
Convert UsersRequest to use new path construction logic