decoding a list of bits according to a code tree.

After a bit of a struggle, I'm going to assume that a code tree made up of
a single Leaf is not a valid tree, and that's why I couldn't make the ignored
tests pass. This works otherwise and decodes the secret as 'huffman est cool'.
encode implementation.

Passes existing identity test with decode.
Recursive implementation of codeBits with pat mat (vs built-in methods).
convert CodeTrees to tables using merge that is analogous to makeCodeTree.
quickEncode using tables