VGMSlap R2

• Rewrote screen update code to only write screen areas when the actual chip data changes instead of refreshing the whole thing. Performance is only marginally better overall, but it is much more responsive on under-specced systems.
• OPL2 detection now actually works outside of emulation.
• Disabled interrupt timer mistakenly left on while decompressing VGZs, now it completes a lot faster.
• Improved handling of VGMs that are missing "end of song data" command (0x66).
• Fixed a mistake in sample position calculation; all commands advanced the position counter even if there were multiple commands in one sample. This may have been a contributing factor to the DIVIDER configuration setting making complicated VGMs sound weird, so setting a higher DIVIDER should be less of a problem now!
• Fixed issue where playlist entries would fail to load on some systems.
• Fixed OPL register/data write delays being reversed.
• Error messages related to file loading are more descriptive.