Use upstream C http_parser

[helje5]

We'd like to use the upstream C http_parser instead of the C port (performance, stability, etc). This is easy to when using Swift Package Manager (which can compile C targets). But we also want an out-of-the-box Xcode experience.

Summary: Need to adjust the Xcode project so that the C http_parser can be built as part of it. Needs some module map magic (contributions are welcome :-)