Add get/set_environment_region (#56)

Set the water height with a function. Also added an example for it in the documentation.

docs/lua/lua.md

@@ -54,8 +54,9 @@ All of this is a holdover from when there were only two players. It was a reason
 - [Custom Surface Collisions](examples/big-paddle)
 - [Custom Box Model](examples/custom-box-model)
 - [Custom Player Model](examples/koopa-player-model)
-- [Moonjump](examples/Moonjump.lua)
-- [Instant Clip](examples/Instant_Clip.lua)
+- [Moonjump](examples/moonjump.lua)
+- [Instant Clip](examples/instant-clip.lua)
+- [Water Height Changer](examples/water-level.lua)
 
 ## Example Lua mods (large)
 - [Extended Moveset](../../mods/extended-moveset.lua)