Add Marshal support to Hamster::Hash.
Add a test for marshalling Hamster::Set instances. No changes are required here, as we never use Trie#get; all membership tests are done via #any?.
Optimize marshalling of Hamster::Hash by representing it as a plain ruby Hash, rather than a linked list of tuples. This gives a factor of three speedup on a trivial microbenchmark.
Merge pull request #19 from cstorey/marshal-support

Implement marshal support for Hamster::Hash