Allows for commenting or uncommenting of sexps.

For visual explanation see:
http://endlessparentheses.com/a-comment-or-uncomment-sexp-command.html

Usage: M-x comment-or-uncomment-sexp

Or to make it easier to run, bind it to a key combination:

(global-set-key (kbd "C-M-;") #'comment-or-uncomment-sexp)