Removed render layer feature for ModelWorld.
RenderTarget supports multiple cameras.

Closes #56
Removed player module, since it is obsolete.
Amend to last commit. :(
Implemented attachment flags.

Attachment flags let you specify what parts of solids transformation
you want to copy.  E.g. only its rotation or only its translation.
Fixed typo in notes.
Merge branch 'master' into feature/scenario
Added much more assert statements to Lua scripts.