added figs directory; three figures from Liang & Klein, 2009
Merge branch 'master' of https://github.com/fmof/variational-tutorial
Merge branch 'master' of https://github.com/fmof/variational-tutorial
fixed up ELBO math; added stub model image slide
Merge branch 'master' of https://github.com/fmof/variational-tutorial