ecere/containers: Iterator::Index() now returning false when creating new entry
- Added GetAtPosition() implementation to CustomAVLTree
- Defining index type of CustomAVLTree to be the key type
   (Iterators for CustomAVLTree/AVLTree must now be declared as Iterator<KeyType, KeyType>)
- Added a 'justAdded' return parameter to Container::GetAtPosition()
ecere/containers: Map/CustomAVLTree optimizations
- Index with creation will not scan again to place new item
- Add/Find inner loop optimizations
- Free: Avoid rebalancing for each item