Switch to using standard practices for installing python packages.

Activate the virtualenv in the venv step. This makes it optional as we
are possibly already in a dedicated virtualenv.
Update readme with new (optional) virtualenv instructions
Fix a typo.
Be explicit about the files that can be edited.
Lazy dependency checking for builds.

Moved all internal files/directories to .build directory to keep the top
level clean.

Now that there is requirements.txt and requirements_dev.txt, there is no
need for an optional virtualenv.
Switch to using the virtualenv's version of pycco
Revert hiding the venv directory and update the readme
Merge pull request #70 from njoyce/pip-compatible

Pip compatible