register event listener return $this

registerEventListener() now returns $this for easy chaining
Merge pull request #27 from mrkrstphr/quick-tweak-eventmanager

register event listener return $this
fixed plugin loading bug

Fixed a bug with having plugins in the folder, but none of them selected to be loaded.
Previously, the code would load all plugins available, and ignore the ones enabled in the config.
Merge pull request #29 from mrkrstphr/plugin-fix

fixed plugin loading bug