Add a very simple trie implementation
Use a trie for compression

Good for a ~5x speedup on compression. Pretty good considering this is a
very naive trie.

benchmark                  old ns/op     new ns/op     delta
BenchmarkCompression       18400571      3351157       -81.79%
BenchmarkDecompression     2631175       2652046       +0.79%

benchmark                  old MB/s     new MB/s     speedup
BenchmarkCompression       7.43         40.79        5.49x
BenchmarkDecompression     28.73        28.50        0.99x