Native heartbeats, request ID support, encoding fixes, test reliability

Fixed bugs:

• WebSocket driver does not emit events for heartbeats #116

Closed issues:

• Passing a frozen channel name or name gives an error on the REST client [Reopen] #145
• Passing a frozen channel name or name gives an error on the REST client #132

Merged pull requests:

• Add request id fix for bulk publishes #154 (mattheworiordan)
• Fix race condition in EventMachine #153 (mattheworiordan)
• Add support for WebSocket native heartbeats #151 (mattheworiordan)
• RSC15d test fixes; add (failing) tests for GET as well as POST #148 (SimonWoolf)
• Do not encode strings in-place #147 (mattheworiordan)
• Only resume if connection is fresh (RTN15g*) #146 (mattheworiordan)
• Fix channel history pagination test #143 (funkyboy)
• Fix presence history test #141 (funkyboy)
• Do not encode strings in-place #140 (aschuster3)