MSX MGSDRV music files.

File content can be recognized by the "MGS" file magic:

+0 (3 bytes): magic string "MGS" (ASCII: 4D 47 53)
+3 (3 bytes): version string:
	"304" for v3.04
	"313" for v3.13
	"320" for v3.20 etc.

	I did not see any files with versions older than "3".
	
	There is a compressed variant of the format that compresses
	all the data that follows the text header. (Apparently 
	there was a MGSARC.COM tool to do this.) Compressed files 
    can be recognized the magic string "MSGA", i.e the major
	version number is replaced by "A".


If available, the non-compressed variants of respective music files
are used here (compressed files are used only as a fallback). Available
players seem to support both variants.

Many files found in the wild contain trailing garbage or only differ in 
minor/irrelevant "MGSDRV" version differences. A hash 
based file matching therefore does not work well. To help future 
identification of the actual song creators, the original file names have 
been preserved within the "- unknown" folder (though originally used 
filenames often also differ), also the songs here a grouped into 
game specific folders (to ease searching in spite of the garbage names).

If somebody has a tool to uncompress the remaining compressed files, feel 
free to replace all the respective compressed files! (I saw a tool 
here: https://github.com/digital-sound-antiques/mgsrc-js/blob/main/src/uncompress.ts
but some extensive testing would probably be needed to check if the converted 
files are actually OK.)


Sadly most of the files again seem to be "remakes" of famous 
game music tracks. To me it looks as if this is a recurring pattern in 
all those Japanese MML based music formats :-(