DistanceMatrix -> DissimilarityMatrix, SymmetricDistanceMatrix -> DistanceMatrix

Still need to update unit test code.
fix doctest failing test
update distance module unit tests

Still need to update the rest of skbio to use the new class names.
update rest of codebase to use new names
Fix some minor issues with the docs
Adding percent explained property to PCoA
Fixing PCoA bug on eigvals returned
TST: Add interface to run tests from python

Tests can now be run using:

>>> import skbio
>>> skbio.test()
update "Gain in PD" reference
Adding test case for eigvals bug
Adding ids to the PCoA results
Addressing comments
Solving merge conflicts
ENH: Add test suites and test data to package_data

Before configuring the setup function for skbio, gather the paths for
all the tests and test data.
TST: Remove deprecation warnings

The usage of self.failIf and self.failUnless is soon to be deprecated so
noesetests was raising a few warnings about it.
TST: Add support for NumPy's in-session testing

Tests can now be executed from within a(n) (I)Python session by calling
something like:

>>> import skbio
>>> skbio.test()
.......... .....
XXX Tests OK
>>> skbio.parse.sequences.test()
........ .......

This is as suggested by NumPy's guidelines, see [1] for more information
about this  document for more information about the configuration.

Notes:

The only odd thing is that if we add the few configuration lines as
suggested by Numpy's documentation, then we end up with an error like
this:

>>> import skbio
>>> skbio.test()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/yoshikivazquezbaeza/git_sw/scikit-bio/skbio/__init__.py", line 54, in test
    return Tester().test(level, verbosity)
  File "/Users/yoshikivazquezbaeza/.virtualenvs/skbio/lib/python2.7/site-packages/numpy/testing/nosetester.py", line 146, in __init__
    raise AssertionError
AssertionError
>>>

That's the reason why we are not doing it as the documentation suggests.

[1] https://github.com/numpy/numpy/blob/master/doc/TESTS.rst.txt
Merge branch 'master' of git://github.com/biocore/scikit-bio into numpy-testing

Conflicts:
	skbio/core/__init__.py
	skbio/draw/__init__.py
	skbio/format/__init__.py
	skbio/maths/__init__.py
	skbio/maths/stats/__init__.py
	skbio/parse/__init__.py
	skbio/util/__init__.py
Returning also 0.0 eigvals
MAINT: Remove retrieval of tests and data …

@Jorge-C noted that there's no need to include the filenames of the
tests in the package_data parameter as there's an __init__.py file being
included in each test suite already. As for the test data, given that
the only module that relies on test data is ordination, it is better to
hard-code the path instead of retrieving the information module per
moduel.

Fixes #247
STY: Remove new line at the end of __init__.py