New tutorial and opcode additions

A new tutorial about subtractive synthesizers was shared by DSmolken's sample instruments experience applied in the Caveman Cosmonaut sample library.
Some fixes and additions were made in our opcode database and in software as well, like the Windows OpenMPT music tracker by sagamusix.
New contributions was provided by other users like jisaacstone, and a big contribution from jpcima for the effects section.
Now we have also a new page for convenience that lists all opcodes present in our database.