Added missing Image methods.
Added missing Group methods.
Added missing ComponentInstance method.
Renamed DefinitionList.erase_memeber! to #remove

In order to make it more consistent with the rest of the API - see `Materials.remove`.
Added missing ComponentDefinition method.
Expanded description of `#glued_to`.
Merge pull request #1 from thomthom/master

Notes on Point3d and Vector3d.
Merge pull request #2 from thomthom/definitions

Added notes on definitions and instances.
Merge pull request #1 from dbowring/master

Pulling latest upstream changes.