Now using py.test for unit testing

- Also added some tags and signal names to builder
  for easier debugging in some cases
- Running with multiple simulators and neuron types
  is done with py.test's funcargs mechanism;
  see http://pytest.org/latest/funcargs.html
  - Additional neuron types are tested in several cases
- Some renaming and cleanup in tests
- python setup.test still works with setuptools,
  but not with distutils. Install should still work though.
Renamed white_noise to whitenoise
Removing .py examples

- I'll add a function to generate these from the .ipynbs
Added PEP8 to testing via pytest-pep8
Added docstring for Simulator

- This shows up when doing py.test --fixtures
Using pytest.mark.parametrize in test_ensemble
Now using tox for testing

This makes it easy to know if your changes will work on Python 2.6,
2.7 and 3.3 without having to push up to travis-ci.

Now, if you pip install tox, you don't need anything else installed;
you can just run `tox` and it will set up a 2.6, 2.7, and 3.3
environment for testing. tox will work just fine in a virtualenv too,
so no changes required if you already have a virtualenv set up.

- .travis.yml uses tox now as well
IPython notebook examples now checked

- Make sure they have no output
- Make sure they don't raise exceptions
- Right now, marked as expected failures
python setup.py test now uses tox
Updated all examples to new syntax

- They all run without exceptions on 2.6, 2.7 and 3.3
Test running improvements (flake8, coverage)

- tox only runs pep8 once, in the pep8 environment
  - Now uses flake8 instead of pep8, which is more comprehensive
- travis-ci should collect coverage information in Python 2.7
  - Also sends it to coveralls.io for visualization
- travis-ci (and locally running tox) now accepts / recommends
  parallelism (if pytest-xdist is installed) with
  `tox -- -n <num_cores>`
- travis-ci using wheels because building is too slow
Added check for cyclomatic complexity

- Simplified some overly complex functions,
  told flake8 to ignore others
Added delay_node example
Using matplotlib master branch

Because of how tox invokes pip, using the version in PyPI
won't work, as it tries to pip install numpy and matplotlib
in the some invocation. Recent versions of matplotlib have
fixed this issue, so for the time being, we'll recommend
the latest matplotlib in requirements-test.txt so that
tox works.