Added tooltips that show for a second or two when the user changes menus.

Also added code for playing different tones on the speaker.
Made the scroll-back buffer 256 lines, taking up 5KB of RAM.

Easier to implement than before because the byte will now automatically
wrap around from end to beginning with no additional code.
Corrected the tones to represent a typical 12-interval scale.
Merge branch 'features/final-fixes' into development