examples/CMakeLists: Disable fonts example

* This ought to be re-enabled upon rebasing feature/Input onto the dev
branch.
Input: Finish implementing the majority of SDL2 events API

* Relocate Event union to include/nomlib/system/events/Event.hpp
* Introduce FingerEvent struct.
* Introduce FingerTouchEvent struct.
* Introduce Gesture struct.
* Introduce QuitEvent struct.
* Introduce TextEditingEvent struct.
* Introduce TextInputEvent struct.
* Introduce WindowEvent struct.
* Introduce initial implementation for finger touch & gesture events
(SDL2 API).
* Introduce initial implementation for text input (SDL2 API).

* Finish implementation of window events (SDL2 API).
* Clean up SDLApp a bit; update documentation comments, re-arrange
method order.
SDLApp: Initial input mapping implementation
types: Introduce NOM_TIMESTAMP macro
Input: General clean up on recent refactoring
Input: Additional refactoring & clean up

* Move SDLApp::poll_events to Input::poll_event as a protected virtual method.
* Replace all instances of EventType (SDL_Event) with nom::Event
* Rename StateMachine::event to StateMachine::process_events
Input: EventQueue stub file