Added new fan.py
Everything I have from fan.py, up until August 12 truncation.
Removed extraneous/old functions that I no longer have or need.
Now with a few old versions of functions directly copied from old backups of fan.py
Revert "Now with a few old versions of functions directly copied from old backups of fan.py"

This reverts commit 6dba2447aeb20729bdbeac9973afdb6995fcd4b0.
Most minimal, before starting rewriting
More cleanup of preamble.
Starting to rewrite data_prep
Continuing work on utilities.
Finished first simple version of dat_prep
Added ad hoc 'find_desired_grpids_without_snap' because Mark may have deleted his cosmo boxes
Re-added load_grid_data
Re-added _grid_to_kpc
Implemented observational column denstiy vs R and differential covering fraction vs R
Added cumulative covering fraction, and Rudie+12 data points
Added starter code at end of fan.py
Small fixes
End of work-day commit 8/19/14
More little fixes.  grid_sightlines should be working more or less.
Updated Rudie data to better match her paper.