ENH: Add support for file paths in DistancMatrix

This object can now load data given a file path or given an iterable of
strings.

Fixes #233
TST: Add tests for from_file with file path

Add test cases for `from_file` method to check that file paths are
parsed correctly and incorrectly, to achieve this, test is now included
in the data directory.
MAINT: Add the test data to the package
Merge branch 'master' of git://github.com/biocore/scikit-bio into issue-233

Conflicts:
	skbio/core/distance.py
	skbio/core/tests/test_distance.py
ENH: Iterate over, instead of loading into memory

If a file path was being passed to the method, all the contents would be
read into memory, instead, now the file-like object is casted into an
iterable and later closed.
DOC: Fix documentation that referred to a class

The documentation needs to be as generic as possible for a base class as
this same documentation will be shown for subclasses.
Merge branch 'master' of git://github.com/biocore/scikit-bio into issue-233

Conflicts:
	setup.py
TST: Remove constants that were in the test data

@ElBrogrammer annoyingly pointed out that constants being defined in
this file could simply be loaded from the test data to avoid the
duplication of data, I reluctantly changed this and I feel like he is in
a power trip, he has to be stopped.
TST: Add test case for DistanceMatrix.from_file

This test was being neglected before this commit.
TST: Add test to verify the correct subclass

Thanks @ElBrogrammer & @Jorge-C
Merge pull request #255 from ElDeveloper/issue-233

Add support to load DMs from a file path