KeyboardHandler: set saner default keys for gamepad.
KeyboardHandler: add methods to change the keys mapped to joypad buttons.
KeyboardHandler: display key pressed/released only if verbose is set to true.
Move ControllerDevice, KeyboardHandler to Flicky; rename KeyboardHandler to KeyboardBox.
Environment: add conveninence functions for the environment callback.
ControllerDevice: remove get_device_type, change the return type of get_device_capabilities to match what the Environment command GET_INPUT_DEVICE_CAPABILITIES expects.
Engine: implements GET_INPUT_DEVICE_CAPABILITIES.
Engine: store AV info every frame; AudioSamples: store the sample rate.
Engine: ensure av_info is valid before acessing it.
Engine: don't inherit from a Core but contain one.
Engine: replace get_system_info with get_library_name.
Engine: store the system info in a property.
Runnable: add reset.
Runnable: rename get_ips to get_fps. Use reset.
Makefile: build everything (and not just the demo).
Reduce dependencies to build demo.