coyote: CGKML_FILE__DEFINE

Description
This program creates a KML file that can be displayed with Google Earth.
It implements some (not all) of the objects or elements allowed in KML files. For 
reference, see  the `Google KML Reference Documentation `.
Categories
Graphics, FileIO
Examples
To create an image overlay object::
  kml = Obj_New('cgKML_File', 'test.kml')
  overlay = Obj_New('cgKML_GroundOverlay', $
      HREF='myimage.tif', $
      LATLONBOX=[])
  kml -> Add, overlay
  kml -> Save
  kml -> Destroy
Author
FANNING SOFTWARE CONSULTING::
   David W. Fanning 
   1645 Sheely Drive
   Fort Collins, CO 80526 USA
   Phone: 970-221-0438
   E-mail: david@idlcoyote.com
   Coyote's Guide to IDL Programming: http://www.idlcoyote.com
History
Change History::
   Written, 28 October 2012 by David W. Fanning.
Copyright
Copyright (c) 2012, Fanning Software Consulting, Inc.
e purpose of this method is to establish the name of a KML file that is to be written. Optionally,
int attribute can be specified that indicated to Google Earth that is should switch to sky view or
 another celestial body, such as Mars.
Params
class: out, optional, type=structure
    The class definition returned as a structure variable. Occassionally useful.
Keywords
lun: in, required, type=integer
    The logical unit number that the KML file is attached to.
e purpose of this method is to destroy anything we created that may leak
mory or need to be released from use.
e cgKML_FILE class definition module.