- Don't crash when passed an empty string. This translated into an actual core
crash, discovered while fuzzing with afl.
- Taking a slice of length one out of bytes returns an integer, so the check
for trailing period in this function never worked on Python3.
- Add unit tests.
This commit introduces MultiDict, a multi-dictionary similar to
ODict, but with improved semantics (as in the Headers class).
MultiDict fixes a few issues that were present in the Request/Response
API. In particular, `request.cookies["foo"] = "bar"` has previously been a
no-op, as the cookies property returned a mutable _copy_ of the cookies.
