site: update 1.0/1.2 doc images
site: small fix in doc version redirection
http: add `startsWith` method to Uri.Path model
http: add `dropChars` method to Uri.Path model
http: add proper `toString` to Uri.Query.Empty

It was rendering `Uri()` before, now it renders the empty string
routing:  change PathMatcher.apply, add PathMatcher.provide method, cosmetic improvements

For PathMatcher, change `def apply[L <: HList](prefix: String, extractions: L): PathMatcher[L]` to
`def apply[L <: HList](prefix: Path, extractions: L): PathMatcher[L]`
docs: improve spray-caching documentation
servlet: improve ModelConverter, add tests, fixes #318