API: cache is now by tip
ENH: smarter tip and non-tip lookups
merge fix
Merge branch 'master' of github.com:biocore/scikit-bio into cache_fix

Conflicts:
	skbio/core/tree.py
ENH/API: assign_ids now matches IDs from index_tree, to_array now
returns an array representation of the tree
Merge branch 'master' of github.com:biocore/scikit-bio into to_array
Merge branch 'master' of github.com:biocore/scikit-bio into to_array

Conflicts:
	skbio/core/tests/test_tree.py
Merge pull request #320 from wasade/to_array

To array