This commit modifies request routing in a backwards incompatible manner.
The change is summarized as: trailing slashes are now significant and
never transparently disregarded. This has the following implications,
all representing behavior that differs from that before this change:
* Route URIs with trailing slashes (`/foo/`, `/<a>/`) are legal.
* A request `/foo/` is routed to route `/foo/` but not `/foo`.
* Similarly, a request `/bar/` is routed to `/<a>/` but not `/<a>`.
* A request `/bar/foo` is not routed to `/<a>/<b>/<c..>`.
A new `AdHoc::uri_normalizer()` fairing was added that recovers the
previous behavior.
In addition to the above, the `Options::NormalizeDirs` `FileServer`
option is now enabled by default to remain consistent with the above
changes and reduce breaking changes at the `FileServer` level.
Sergio Benitez