Support vendor handlers, processors and formatters.

The need came out of having to implement `CakeEmailHandler` into the plugin itself since the [pull request](https://github.com/Seldaek/monolog/pull/162) was [declined](https://github.com/Seldaek/monolog/pull/162#issuecomment-13488664) and rightfully so, since now it supports all other monolog external libraries.