PHP Collection: Manipulate collection objects indexed by names

This class can manipulate collection objects, also known as dictionary objects, like in Java, that store entry values indexed by name keys.

It provides functions to:

- Add entries by name key
- Remove entries by name key or by position
- Retrieve entry values by name key or by position
- Determine whether there is already an entry with a given key
- Iterate over all entries by position order
- Retrieve all entries in a a non-associative array
- Remove all entries from the collection