Added very rudimentary event handler.
Added observing_ptr tests to cmake.
Merge branch 'tests'
Added very rudimentary event handler.
EventHandler kinda works!
Merge branch 'boost_events' of github.com:Gazok/Tank into simple_events

Conflicts:
	Tank/System/EventHandler.cpp
	Tank/System/EventHandler.hpp
Cleaned up events.
Reformatted.
Fixed cmake file.
Added some stuff.
Removed empty file.
Implemented eventhandler in game loop
Merge branch 'simple_events' of github.com:Gazok/Tank into simple_events
Made EventHandler::connect return std::unique_ptr

EventHandler::Connection currently has no default constructor, and cannot be
stored as an uninitialized member variable. Hence return
unique_ptr<EventHandler::Connection> to allow this.