DOC: Add doctest for pwmantel
DOC: add additional doctest examples to pwmantel

Showing/describing usage of ``lookup`` and ``strict``.
Move dm-matching code into mantel

Previously was in pwmantel, but it makes sense to support matching of distance matrices in both functions. Minimal updates to tests and docs to get things passing again. Still need additional changes to unit tests, doctests, and documentation.
Move shared test data into base class

Prepping for refactoring of unit tests.
Add unit test class for _order_dms

This function is more complicated now so it makes sense to explicitly test it.
Add error-path tests for _order_dms
Remove duplicate test data in MantelTestData
Add _order_dms tests for reordered/mismatched dms
Add remaining unit test for _order_dms (testing id lookup)
Add checking of n value being returned by mantel
Add reordering/nonmatching/lookup tests for mantel function
pwmantel now accepts array_like as input
update docstrings/doctests for mantel and pwmantel
Fix doctest, pep8, and flake8 errors
DOC: add changelog mention of mantel/pwmantel changes
"data frame" -> ``DataFrame``

Thanks @gregcaporaso
Refactor type-checking logic in _order_dms.

Refactored logic to put TypeError at the top of the function. Thanks @wasade!
Move ID mapping code into _remap_ids.

This removes some duplicate code and allows for more informative error messages. Thanks for the suggestions @gregcaporaso and @wasade!
Merge pull request #619 from jairideout/issue-443

Various improvements to skbio.stats.distance.mantel/pwmantel functions