ENH|API: IO registry exists
STY|API: pep8 and moved IO exceptions to skbio.io
TST: fixed StringIO for python3
TST: more python3 fixes
TST: assertTrue had 2 args, moved testclasses out of setup
DOC: added documentation about io
STY: minor changes
Merge branch 'master' of https://github.com/biocore/scikit-bio into issue564

Conflicts:
	skbio/alignment/_alignment.py
	skbio/stats/distance/_base.py
	skbio/stats/ordination/tests/test_ordination.py
	skbio/tree/_tree.py
	skbio/tree/tests/test_tree.py
	skbio/util/__init__.py
DOC/ENH: loosened concept of filehandling in procedural implementations and added convenience identifier for blank files
TST: 100% branch coverage
Merge branch 'master' of https://github.com/biocore/scikit-bio into issue564
TST: fixed for python 3
Fix unit test name in pairwise tests
Remove duplicated warnings.simplefilter calls

...in favor of setUp/tearDown methods.
Add assert_warns call to Alignment.toFasta test
Add assert_warns calls to beta-diversity tests
API: registration now abstracts file opening
DOC: Add doctest for pwmantel
DOC: add additional doctest examples to pwmantel

Showing/describing usage of ``lookup`` and ``strict``.
Merge pull request #615 from jairideout/issue-479

Remove duplicate code in unit tests used to ignore warnings