Add missing methods to Sprite
Don’t overprint the 'Examining' lines in gen_docs.rb
Hm. I wanted to make an animated moon, but I can’t get GIMP to import the SVG moon directly, and scaling the PNG looks bad.
Add replacement for MRuby’s Data_Get_Struct that doesn’t do bad typechecks.

Data_Get_Struct doesn’t understand C++ inheritance and therefore
fails if you tell it to "cast" to a superclass instance pointer.
Replace Data_Get_Struct with our more permissive Get_Data_Ptr
Add missing Enemy methods
Add enemy die event
Add missing MovingSprite methods