setup.py: Add 'pytest' and 'ipdb' to deps

Fixes GH-8.
Don't patch things unless --ipdb is passed
Add tests
Add tox.ini for tox
Merge pull request #18 from msabramo/add_tests

Add tests
Merge pull request #16 from msabramo/add_install_requires_pytest_and_ipdb

setup.py: Add 'pytest' and 'ipdb' to deps
Merge pull request #17 from msabramo/dont_patch_when_ipdb_arg_not_passed

Don't patch things unless --ipdb is passed