Fixes issue #496

Simple fix for #496, which seems like a typo error. Credit for fix goes to wasamasa on irc.freenode.net #emacs, who found the error while I was flailing about trying to repro :D
Add helm mental model FAQ.
Use upstream markdown-pp.
Merge pull request #497 from ravaa/master

Fixes issue #496
* helm.el (helm-multi-key-defun): Use cl-declare to avoid update of autoload adding incompatible function-put (#496).
* helm-config.el: update autoloads.