Merge IPS's excalibur
Make happy stick consistent with excalibur
Mention excalibur in README.md
Merge almost all remaining changes by IPS (from Beta 2 add-on upload)

Without cannon (I think thunderstick animation is already overused),
without +5 damage shop items (I think it makes it too complicated),
without teleport price reduction (I think it's already OK and might
need to be increased instead).