* Trailing slashes are now allowed in all normalized URI paths, except
for route attribute URIs: `/foo/` is considered normalized.
* Query parts of URIs may now be empty: `/foo?` and `/foo/?` are now
considered normalized.
* The `base` field of `Catcher` is now only accessible via a new
getter method: `Catcher::base()`.
* `RawStr::split()` returns a `DoubleEndedIterator`.
* Introduced a second normalization for `Origin`, "nontrailing", and
associated methods: `Origin::normalize_nontrailing()`, and
`Origin::is_normalized_nontrailing()`.
* Added `Origin::has_trailing_slash()`.
* The `Segments<Path>` iterator will now return an empty string if
there is a trailing slash in the referenced path.
* `Segments::len()` is now `Segments::num()`.
* Added `RawStr::trim()`.
Resolves#2512.
Sergio Benitez