Fix note limit

Maximum note was A7 instead C8 should have been.
Add sequence max length constant
Implement envelope sequence commands
Implement group slots
Remove unused file
Implement sample loading from external audio file
Normalize loaded sample
Set missing pitch value
Remove truncate option
Implement wave file output
Fix wrong variable
Fix wrong argument order
Silence warning
Remove unused variable
Add missing return
Implement sample offset and end commands
Implement BK_SAMPLE_RANGE attribute

Remove previous BK_SAMPLE_OFFSET "do" and BK_SAMPLE_END "de" commands in favour
of new command "dn".
Rename sample pitch command from "p" to "pt"

Now this is the same name as for the notation commands.
Cleanup code
Update submodule