Provide versioned specification documents

[jpcima]

Hello. Do you mind archiving different finalized versions of file specifications as distinct documents?
This will be easier, and less confusing, than examining a commit history.

There was a request for BambooTracker instrument importing, and I would like to add the support, for old files as well as current and future. Wohlstand/OPN2BankEditor#71

[rerrahkr]

Thanks for your request. I will try to make a new directory specs and archive old and current specifications.

[rerrahkr]

I added at bb98a73.

[jpcima]

It's very nice, thank you.