Add various configuration options to README

Also add a description about the solarized theme.
clone via https - ssh not working anonymously
Add details to README on creating themes.

Closes #662.
Merge pull request #664 from vertti/patch-1

add details to README on creating themes
Merge pull request #657 from asmaps/master

README: clone via https
readme tweak #660
merge readme conflict
Merge branch 'update-readme' of https://github.com/aethanyc/reveal.js into dev
additional config valeus in readme, remove duplicate value, fix commas