Constraint code ported from WebAPI2. Tests are new.
Also a bunch of misc cleanup for constraints.
- Move IRouteConstraint to abstractions
- Fix namespace of a constraint
- Some general style cleanup
- use RouteValueDictionary in the public API
This is useful for a variety of interesting scenarios in link generation
where a default value doesn't appear in the route template as a parameter.
This can be used to implement the desired behavior for areas - where the
'area' key is sticky.