Sync `c9/engine.io`, `c9/engine.io-client` with `LearnBoost/engine.io`, `LearnBoost/engine.io-client`

[cadorn]

To sync these repos all patches in our repos should be contributed upstream via the following issues:

• Get rid of path, just keep resource and identify engine.io in query string socketio/engine.io#116
• Regular expression & check function support for resource socketio/engine.io#117
• Multiple attachments to the same server socketio/engine.io#118

The goal is to get rid of our clones and use engine.io packages from NPM directly again.

Most of this code was part of socketio/engine.io#76 which will not land as-is and has been segmented into above issues.