Extra Python Collections - bags, setlists, RangeMap and IndexedDict

 collections_extended is a pure Python module with no dependencies providing:
 .
  * a bag class, also known as multiset,
  * a setlist class, which is a unique list or ordered set,
  * a bijection class, RangeMap which is a mapping from ranges to values,
  * a IndexedDict class, which is an ordered mapping whose elements can be
    accessed using index, in addition to key.
 .
 There are also frozen (hashable) varieties of bags and setlists.
 .
 This package installs the library for Python 3.