beginning of a low-level tree class to support induced_tree
moving non-OTT code to phylo/tree
simple iteration and test
simple iteration and test
another test added, but needs verification of postorder
bug fixes in new code and tests that revealed them
restoring test that was removed during debugging
Improving performance with better list operations

pop() and extend are faster than pop(0) and prepending.

making each node remember its index in the parent's _children
array is a pain from the standpoint of more bookkeeping, but
removes an O(n) operation in replace_child.
added reversed children iterator to make the postorder traversal more natural fit for the data model
using builtin next for Py3 lack of .next in generators
correcting tests
preorder iteration
preorder iteration
write_newick and before_after_applyw
simple newick tokenizer - not tested
some test of tokenizer ability to deal with ws and comments
quoted tokenization
tokens and new test
branch length
newick events interface