[base] adds Severity 'diag'. fixes #86
[http] improved HTTP protocol error handling.
[flow] extends match-syntax to allow multiple labels for a single case.

Example:

    handler main {
      match req.path {
        on '/chat/send',
        on '/chat/listen',
        on '/chat/activity' {
          chat_backend;
        }
        else {
          app_frontend;
        }
      }
    }
match syntax adaptions
[flow] Improved semantic check on potential unknown symbol uses for possible builtin handler/method calls.
[x0d] do not enable Flow IR optimizations by default (for now)
[http] HttpConnection: code cleanup - removes unused flag 'IsResuming'
[http] HttpMessageParser: ensure parser state is always set *before* invoking onMessageEnd()
TODO-update