Allow to specify paths / support --help

[blueyed]

It should be possible to run it on a single file / path only.

Additionally, dodgy --help should not run, but display help.

[ricco386]

If dodgy is used by executable script user has no idea how to use it. So the --help would be great UX improvement. If you also add the ability to specify path would be a plus for the user so he doesn't need to change directory in order to run the checks.

I had to look into the source code in order to understand how to use it...