ENH: Add iter_regex and find_features

Fixes #612. Adds iter_regex to skbio._sequence.BiologicalSequence and
find_features to skbio._sequence.NucleotideSequence. Supported features are
currently purine_run and pyrimidine run, but more can be added by specifying
additional regular expressions.
Simplify the regex considerably

Not quite sure what I was thinking with that one
Add option to allow gaps
Move feature types into class hierarchy

Also add some additional tests
Merge branch 'master' of https://github.com/biocore/scikit-bio into issue-612

Conflicts:
	skbio/sequence/tests/test_sequence.py
Update _base.py

IPython.display replaced by IPython.core.display as IPython.display does not exist in recent version of IPython
source: http://ipython.org/ipython-doc/2/api/generated/IPython.core.display.html
skbio.draw.boxplots hack for empty distributions

Empty distributions are plottable in mpl < 1.4.0. In 1.4.0, a ValueError is raised. This has been fixed in mpl 1.4.0-dev (see https://github.com/matplotlib/matplotlib/pull/3571). In order for skbio.draw.boxplots to support empty distributions across mpl versions, empty distributions are replaced with [np.nan]. See https://github.com/pydata/pandas/issues/8382 and https://github.com/pydata/pandas/pull/8240 for details.
TST: remove unit test docstrings from test_distributions.py
Add tests and comments for np.nan hack
TST: travis tests against mpl < 1.4.0 and latest version
Merge branch 'master' into issue-649

Conflicts:
	setup.py
	skbio/draw/_distributions.py
TST: update dep versions for consistency

Based on @Jorge-C's suggestion
Revert "TST: update dep versions for consistency"

This reverts commit 1e12536f793b2c59878078c88447349432b67e15.
Merge pull request #700 from jairideout/issue-649

Support newest matplotlib release
Update test_ordination.py

IPython.display replaced by IPython.core.display
Merge pull request #699 from jradinger/patch-2

Update _base.py
Change import of re

Thanks @ebolyen and @jairideout
Merge pull request #613 from adamrp/issue-612

ENH: Add iter_regex and find_features
Merge remote-tracking branch 'upstream/master'
Deleting reference to old clustal functions