benchmark mode that, when enabled, tries to decode frames as fast as possible and prints "frame per second" messages to the JavaScript console

Signed-off-by: Dominic Szablewski <mail@phoboslab.org>
fix printing to console for Internet Explorer 10, make fps available via this.benchfps

Signed-off-by: Dominic Szablewski <mail@phoboslab.org>
Cosmetics