Make completely necessary changes to the change log

- Fix whitespace
- Fix spelling
HANDLE_* (mostly) quotes spaces and special characters

With the exception of the command, because it doing so does not
currently play nice with Windows.
Clarify prompts.tra
Fix and clean up ADD_MUSIC
Document ADD_MUSIC
The beginnings of a regression-test suite
Optimisations to DECOMPRESS_BIFF
EXTEND_MOS makes one less assumption
Change-log for the EXTEND_MOS change
Version 232.01
Add modified-by-me notice
HANDLE_* use strong quotation on *nix
Version 233.00