Fix for RangeFan.py

Deconflict 'range' reserved Python keyword with internal variable.
Renamed to 'dRange'.
Fix problem with file RangeRings file name

File name mismatch between GitHub (RangeRings2.py) and ArcGIS.com
(RangeRings.py) caused problems when user downloaded GitHub to update
template.
Merge pull request #48 from mfunk/master

Fixing problem with Visibility And Range tools