Add AdLib Tracker II formats (A2I, A2B, etc.)

[Wohlstand]

There are native bank and patch formats used by AdLib Tracker II software.

Specification: http://adlibtracker.net/files/techinfo.htm Source code of AdLib Tracker II (FreePascal), needed for compression/decompression: http://adlibtracker.net/files/at2_sourcecode_09-09-2019.zip

I started the work at the wip-adlibtracker branch but will continue it soon. Those formats do require the compression algorithm being implemented. There are pascal codes adt2pack.pas and depackio.pas which are contains compression and decompression codes.