Make package pip-installable.

[sguermond]

• Removed importlib from install requirements in setup.py, was causing error
• Delete PKG-INFO file (is auto-generated with updated information when installing)
• Added instructions for installing via pip in README

[peter17]

Hi sguermond,

Thanks for this PR. Unfortunately, the Travis tests fail.

Also, importlib is needed by Pijnu (see generator/generator.py)

Please note that pijnu is already installable by pip install pijnu. Did you encounter any problem in installing it this way?

Best regards