Adding partial man page. Not quite half done...
* Finished section on scan options.
* Finished options sections for list, dupe_files, and dupe_trees.
* Finished options sections for diff, rm, and checkdb sections.
* Added license info to tops of all code files.
* Updated summary line.
* Tweaks to man page. Essentially finished.
Merge branch 'dev' of https://github.com/jsbackus/bit_rot_detector into dev