added inverted power potential (incomplete)
make the git revision visible from within pele

setup.py identifies the git revision and saves it in a created file
pele/version.py

the git revision can be found by

    import pele.version
    print pele.version.git_revision
wrapped inversepower, added cpp test (incomplete)
added python test, not working
added tests
fixed inverse power and cpp tests
fixed python tests for inverse potential
Merge branch 'master' of https://github.com/pele-python/pele into inverse_power_potential
fixed documentation and removed tabs
fixed one more indentation issue
fixed indentation issues
fix indentation issue
fix a few more indentation issues
Merge pull request #59 from smcantab/inverse_power_potential

Inverse power potential