Merge pull request #71 from jhmatthews/dev

Moving estimators increments from radiation into subroutines (estimators for PPL ionization solver and IP)
Changes to compute zeta to deal with fix #72
Cleaned up some comments in radiation
Cleaned up zeta.c, relates to #72
commented out GS log statement
Converted frequencies to rest frame of cell in radiation.c
Added some comments
Merge pull request #74 from jhmatthews/freq_hotfix

Fix for Bug #73. Now use frequency shifted to frame of cell then averaged
Added levelpopulation option for macro atoms to py_wind for each cell for tests
Merge branch 'dev' of https://github.com/agnwinds/python into dev