This commit also adds the `base` field to `Route` which allows the
base mount point to be retrieved. Finally, this commits adds an
implementation of `FromRequest` for `Route` which returns the active
route if one is available or forwards otherwise.
This commit is a breaking change: it makes `Request` and `MockRequest`
invariant over the lifetime `'r`. While this shouldn't affect most
applications, it may affect some.
Resolves#108.
Sergio Benitez