refactoring of node-cef to support heka

This is the reworked patch to get heka-node and node-cef to play nice with each other.

I've added an error-back mechanism so that node-cef can pass errors back to something better than console.error. 

I've also added a property to the config so that a custom syslog factory can be provided which effectively gives us the ability to use heka as a transport instead of syslog.

Detailed changes:

* added test and code to catch extension errors
* added code and tests to support a custom error_back function to
  capture errors during CEF formatting.  Errors will be passed back
  through the error_back along with a context so that offline debugging
  is possible
* ignore vim swap files
* added test and code to pass in a custom log_factory through the
  syslogconfig object so that an alternate syslog-ish transport can be
  provided