Is the info on keys sounds absent from the manual? My bad.
Just add sounds named "Hp1.wav" or "Key1.wav" etc. Where you can replace 1 with another key or hp number (1-5 for hp and 1-3 for keys). I'll make sure to add import buttons for those.
Melee weapon not dealing damage to decorations might be a bug. Try making their radius smaller. If it helps, then this is indeed a bug. I'll check it out.
"Menu.script" is a special script and doesn't really reflect on how the whole scripting system works. Basically to show some text you need to add a script with the name of the map. It will be loaded automatically. Then put this inside:
text "Hello world!"
map start
and it should work.
1.04 is the closest to the current version. There are some changes in scripts but the overall reference is recent enough to help you writing simple scripts.
UPD: I checked the code and it doesn't seem like a bug. Do you have all the sprites imported?