* Limit max number of listeners when #max_listeners is provided

* Prevent override listeners limit

* Move Emittr::Setup specs to its own file

* Include setup class only inside Emittr::Events

* Rename #listeners_limit to #max_listeners

* Manage all listeners on Listeners class instead of Setup

* Add #max_listeners implementation on Listeners class

* Remove needless "return" from #max_listeners method

* Test #max_listeners behavior on both listeners and events specs

* Set #max_listeners when build new Emittr::Emitter object