add settings configuration object

[jonathanargentiero]

This PR is intended to implement the possibility to override default options. I called the configuration object settings to avoid confusion with the options parameter defined in zongjiManager(dsn, options, onBinlog). Available options are described here and can be useful in many scenario.

A documentation update could be necessary to provide information about this configuration object.

[jonathanargentiero]

Usage example

var mysqlEventWatcher = MySQLEvents(dsn, {
  startAtEnd: false // it overrides default "true"
});

[spencerlambert]

This looks good. Do you mind updating the README.md file, describing this change?

[jonathanargentiero]

@spencerlambert done. :)