Add markers around the description to help MELPA

This should enable the description at http://melpa.org/#/parenface
Support Emacs 24.4 and a workaround for issue #7

lisp-font-lock-keywords-2 has become an obsolete variable in Emacs 24.4
so use lisp-cl-font-lock-keywords-2 and lisp-el-font-lock-keywords-2
instead.

Use lexical binding paren-face-add-support to help avoid warnings about
accessing said obsolete variables.

Disable the parenface in slime-repl-mode until we come up with a fix
for issue #7.
Merge pull request #8 from luismbo/emacs-24.4-support-and-more

Emacs 24.4 support and a workaround for issue #7