Support for .sav RAM files loading in SDL

See merge request !28

This is done at a rate of every 5 seconds.

Make dmg-audio tests pass

See merge request !26

There are many quirks to how this works but the unfreeze and thre length clock on enable are the most important ones.
For more information on these options check https://github.com/retrio/gb-test-roms/blob/master/dmg_sound/source/03-trigger.s.

We're currently in the 02-len ctr.s test.

Making them smaller.

Merge branch 'joamag/audio-tests' of ssh://gitlab.stage.hive.pt:2222/joamag/boytacean into joamag/audio-tests

Also added support for image saving.

Test for test_blargg_instr_timing.