fix logic error 'array access results in a null pointer dereference' refs #187
small refactoring for fix logic error 'array access results in a null pointer dereference'
Use a weak reference for the delegate.

Fix #78.
Merge pull request #193 from siberianisaev/issue_187

fix logic error 'array access results in a null pointer dereference'
Merge pull request #200 from paulyoung/delegate-weak-reference

Use a weak reference for the delegate.
Add `sendPing:` method and a delegate method for received Pongs

Also added some sample code in the sample chat app.

Simplify ping/pong handling

Timing is an application-level thing

Style updates
Merge pull request #186 from cbrauchli/add-ping

Add ability to send a ping message and notify delegates of "pong" responses
merging with upstream