Use Hashmap instead of Map

[hellerve]

This PR implements an experimental migration from Haskell's Map (balanced binary tree) to a HashMap (Patricia tree) for hashmaps.

We should do some performance measurements to see how this a affects zepto's overall performance.

[hellerve]

And, because I like Bagwell's data structure ideas, maybe it would also make sense to investigate a Hash Array Mapped Trie.

[hellerve]

I had an idea how to hash complex numbers yesterday evening. It might be a really bad idea, but maybe something like the following would work:

hash  = hash(imaginary) & hash(real)

I would think that the distribution of hashes is uniform, but I can't whip out a formal proof (mostly because I suck). Any comments regarding how my understanding is flawed or not are welcome.