Port tests to use nose

This has a couple of benefits..
 * no need to create boilerplate test_*.py python modules for doctest test cases; nose will discover them automatically
 * since splparser is only imported once instead of in each test case, it's significantly faster (2s vs 1:30 on my machine)
 * nose has many other nice features too...

Also,
 * Add requirements with best guess of version deps
 * Add traverse-namespace option to nose, which makes naming tests by submodules work