Return to fset-ing `describe-bindings'.

Just remapping describe-bindings does not make keymap C-h use
helm-descbinds.

Closes issue #5.

Signed-off-by: Michael Markert <markert.michael@googlemail.com>
Require 'cl on compile for flet.

Signed-off-by: Michael Markert <markert.michael@googlemail.com>