Add CSV output format support

Add CSV output format support:
   * Add command line option to specify output format.
   * Add date_safe_str to return csv output format dates
   * Add values to shell bags for csv output
   * Add print_shellbag_csv to print out shellbags as csv
Merge branch 'csv-output'

Conflicts:
	shellbags.py
Merge pull request #5 from jasonanovak/master

Output format selection