#78 Allow people to ping "folks"

I propose that if someone writes a message, "folks: blah blah blah", funbot should immediately write "^$folks" or "$folks: $person says blah blah blah" or something like that. Could also interact with the !tell command, but should not happen when "folks" is mentioned in the middle of a sentence.

I added a !folks command. Reopen issue if you have improvement suggestions.