Provides the iradix package that implements an immutable radix tree. The package
only provides a single Tree implementation, optimized for sparse nodes.

As a radix tree, it provides the following:

- O(k) operations. In many cases, this can be faster than a hash table since
the hash function is an O(k) operation, and hash tables have very poor cache
locality.
- Minimum / Maximum value lookups
- Ordered iteration

A tree supports using a transaction to batch multiple updates (insert, delete)
in a more efficient manner than performing each operation one at a time.