Found a case where http_parse_message failed to parse a valid request header and returned null, which ended up in an uncaught exception being thrown by Guzzle.
pecl_http if available to parse HTTP requests (5x faster)
Update ConnectionContext to match latest RFC interface
Removed Guzzle integration test (now using PSR-7 API)
Http components and APIs now use PSR-7 interfaces
No longer using deprecated Guzzle dependency
Use RFC6455 repo for WebSocket message handling
Remove Hixie76 (refs #201)
