Adding tox.ini.

 * Firstly install tox, and run "tox" command.
 * See also http://tox.readthedocs.org/en/latest/index.html

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Closes #6 Changing behavior of python setup.py test.

 * Changed using tox for diffrent Python versions and interpreters.
 * Change using py.test in tox.
 * Append requirements.txt for test requires with travis-ci.
 * Append "Programming Language" to classifiers.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Merge pull request #10 from mkouhei/switch_using_tox

Switch using tox