New features, sync with upstream

[ivop]

Hi,

The last few days I have been working on adlib2vgm. List of changes I made:

• verbose conversion messages under -v option
• enabled messages in loaders/drivers, visible with -d option
• added all adplug loaders of which I could find a sample file
• synced with upstream, lots of fixes in the last two years
• added subsong support
• added looping support
• added GD3 support (metadata)
• fixed low volume on conversions, only one of the OPL2/OPL3 clocks is set
• slightly improved timing
• rewrites/simplification of other logic
• added auto detection
• use shorter wait commands if possible
• basic regression test in tools directory
• made code work on big-endian, too
• added option to export gzip compressed .vgz directly
• perhaps more, I forgot ;)

I kept your coding style intact, i.e. true tabs, tab width 8.

You might want to remove the 'not 100% compatible with VGMPlay' remark from README.md. I have not encountered any problems anymore with https://github.com/vgmrips/vgmplay or https://github.com/adplug/adplay-unix/ .

If you want further things done before merging, please let me know.

Kind regards,
Ivo

[ReimuNotMoe]

Thanks