Add FleepHookHandler

This commit adds a Handler for sending logs to fleep.io
conversations using their Webhook integration
(https://fleep.io/integrations/webhooks/).

The code has decent line coverage, coded against PSR-1/PSR-2.

![fleep](https://cloud.githubusercontent.com/assets/469120/4081472/01e8cc7e-2ee8-11e4-8351-bf73713bd2af.png)
I added the example to emphasize that this is only the token, not the full hook URI, which is provided by Fleep when creating the hook. Might avoid some seconds of confusion for developers who only peek at the constructor phpdoc (from IDE)?