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 it to test the constructor (@see testConstructorSetsExpectedDefaults). As for other uses, you're probably right.