Change camstats so that output can be written to any type of text file, along...

Change camstats so that output can be written to any type of text file, along with some documentation changes. Reference Redmine ticket #175.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@6225 41f8697f-d340-4b68-9986-7bafba869bb8