Support initial route and link to route

[albertogasparin]

Couple of new APIs to allow better and future optimisations:

• Link prop to now accepts a route (as object or dynamic import), and will automatically build links using params and query additional props
• pushTo and replaceTo actions to push/replace by providing a route instead of a string
• Router prop initialRoute to avoid scanning all routes on initialisation

Moreover matchRoute result is now cached, so looking for the same location will avoid looping through all route definitions over and over.

TODO:

• [x] add examples
• [x] add docs