Add flag and feature to skip certain files and directories

[Shabirmean]

• Introduces a new flag to take in files/directories to be skipped
• Doesn't support any regex, does a simple contains()
• Can exclude whole directories or files

[lukehinds]

I was about to work on a similar patch. It would be nice to able to skip by extension, rather then having to spell out names.

for example, .md / .cfg / yml / toml etc

[willnorris]

alternate implementation of this feature was added in #84