Merge pull request #2 from polyphant1/8July-void-dist

modified void_distribution.py to incorporate density and class changes
new file powspec_add.py. Small change to comment in cosmology.py
Merge branch 'void_distribution_branch' of github.com:polyphant1/PyCosmo into void_distribution_branch
added powspec_add.py. changed text output in cosmology.py
Delete powspec_add.py~
Merge pull request #3 from polyphant1/void_distribution_branch

Void distribution branch