initial attempt at marking parser
Added newline
Added license and readme. =)
PEP 8 compliance
Add boolean flag for including all nodes

Previously, all nodes were output, including whitespace-only nodes and
comments. Now, these are hidden by default unless the -a flag is passed.
Make usage message correct
Make script executable
General code cleanup
Merge pull request #4 from STIXProject/marking_parser

Add script that parses and displays STIX data markings and the marked data.