parameterised route creation

[jedws]

we have a few cases where we have routes that share a common root. At the moment it is non-trivial to add a common root part to a parent.

as all descendants of Path all define the same builder (:/:) methods, simply defining them on Path itself allows us to very easily create builder methods that use those on any Path:

def addRoot[P<: Path](p: P) = "root" :/: p

[noelwelsh]

I'll take a look. Routes support some composition, but perhaps not in the best places.