Clarify what stream_body is doing
Add R16B03-1 to the list of releases to test
Add and document the new multipart code

The old undocumented API is removed entirely.

While a documentation exists for the new API, it will not
be considered set in stone until further testing has been
performed, and a file upload example has been added.

The new API should be a little more efficient than the
old API, especially with smaller messages.
Use the INLINE_LOWERCASE macro in the request parsing code

Since I made it for similar code in cowlib, let's use it here too.
Update copyright years
Allow empty passwords when parsing Basic authorization header