Replace loop with call to raw_ostream::indent().
Don't crash if we aren't tracing and we timeout / run out of runnables.
Print timeout / run out of runnable messages when tracing is disabled.
Add option to display cycle count in trace.
Add support for --version.
Switch AXE over to using SDL2 instead of SDL.

One benefit is that SDL2 no longer overrides main(), so axe doesn't appear
as an icon on the OS X dock unless the lcd screen peripheral is used.