Fix #15 - installing from pip and easy_install

[ccpost]

• Ensure that the build_ext task is called to generate SWIG .py files
  before the Python copy step happens and we miss packaging and
  installing the generated files.
• Wrap the install command for use with pip. This is a bit of a
  hack because setuptools looks at the stack frame to determine if it
  was called from the setup function, and wrapping it would break that
  behavior.
• Wrap the bdist_egg command for use with easy_install.

Bear in mind that I'm no setuptools / distutils expert. This is the combined result of a bunch of Googling and some source diving into setuptools / distutils. Interesting references about this problem include:
http:https://stackoverflow.com/questions/10559589/adding-output-file-to-python-extension
http:https://stackoverflow.com/questions/29477298/setup-py-run-build-ext-before-anything-else
http:https://bugs.python.org/issue7562
http:https://stackoverflow.com/questions/12491328/python-distutils-not-include-the-swig-generated-module
http:https://stackoverflow.com/questions/17666018/using-distutils-where-swig-interface-file-is-in-src-folder/26556654#26556654

[coveralls]

Coverage remained the same at 18.295% when pulling 41ca7d1 on ccpost:fix/pip-install into f793225 on LudovicRousseau:master.

[LudovicRousseau]

On Mac OS X 10.11 using Python 2.6 (default)

• Installation using pip still fails.
• Installation using easy_install works