New puzzle, music, editor improvements

Although it was actually added a week ago, I didn't announce on itch.io that there is (finally) a new puzzle!

Additionally, today's update (v1.9.5) brings other changes, along with many code editing improvements:

• Added one new music track
• Added block comment/uncomment
• Added block indent/unindent
• Added auto-indenting
• Added optional support for inserting tabs
• Added in-code/persistent breakpoints (prepend "!")
• Added auto-select for compilation errors
• Added click-to-toggle-watch for arbitrary memory cells
• Added Errata section to manual
• Fixed scrolling when starting/stopping debugging
• Fixed "program too large" error message
• Fixed small bugs in the "Multiplication" and "Mode" tasks
• Updated charts