Minor fixes

- No need to mention "Emacs" in the package description line
- Declare dependency on Emacs 24
- Don't use unsafe local variable (put something [like this](https://github.com/purcell/emacs.d/blob/master/lisp/init-lisp.el#L247-L252) in your emacs startup file instead)

In connection with https://github.com/milkypostman/melpa/pull/2203.