Add Remove() function to red-black tree iterator

[virtuald]

Fixes #28, using idea as suggested by @raltnoeder . Seems to work.

[emirpasic]

This would need to implemented on the Container interface level, i.e. for all data structures. Removing elements during iteration should be reconsidered carefully and invovle locking mechanisms

[emirpasic]

This would need to implemented on the Container interface level, i.e. for all data structures. Removing elements during iteration should be reconsidered carefully and invovle locking mechanisms