py.test-base test runner.

This requires some minor fixing-up of python namespaces to avoid namespace
conflicts with pre-existing py module.
Install py.test via pip during build
Remove dependency on nose
Moving requirements.txt and adding comments following feedback at https://github.com/oxtopus/nupic/commit/fb23e3558f7bda214ba424ae26bdced47f0419a3#commitcomment-3705875
Moving run_tests.py to bin/ to match post-build testing instructions in README.md
Run tests in verbose mode
Merge pull request #131 from oxtopus/pytest-requirements.txt

py.test-based test runner