GradientTest: Use set_scale in Margins test
Introduce Point2(int), Size2(int) ctors

* MathTest: Add tests for these new ctors
Image: Fix ::load_memory method

Oops... I was passing a NULL pointer
Install librocket deps for examples
Introduce Size2 division operator
Fix disabling of OSX fullscreen spaces

This must be done before the call to nom::init -- or
nom::init_third_party when not using nom::init -- as the hint
internally depends on SDL's video subsystem to first be initialized.
SDL_helpers: Introduce ::available_render_driver
Use nom::available_render_driver in app ex && libRocket tests
Finish support for SDL2 independent resolution scale

* ttcards.rcss: Declare a default datagridheader tag for font style
used.

* UIContext: Introduce ::debugger_size, ::set_debugger_position; these
are necessary for correctly positioning the visual debugger, relative
to the resolution scale in use.

* libRocketDataGridTest: Use testing resolution of 768x448 && update
style sheets to better match the coordinates used in TTcards.
DecoratorFinalFantasyFrame: Fix out of bounds rendering bug

Account for negative dimensions, otherwise this can lock up the
rendering loop...
InputStateMapper: Ignore key repeat logic unless non-zero (explicit)

This logic change means that by default, keyboard input actions are
triggered whether or not they are marked 'repeating' by the underlying
events subsystem. Otherwise, holding down a key would (by default) only
trigger once, unless explicitly mapped with a key repeat value of one.