Adding sticky navigation option
Turning off sticky navigation if navbar is taller than window

Conflicts:
	sass/_theme_layout.sass
	sphinx_rtd_theme/layout.html
Merge remote-tracking branch 'snide/master' into sticky-navigation

Conflicts:
	sphinx_rtd_theme/static/css/theme.css
Merge branch 'snide-master' into sticky-navigation
Commenting out sticky_navigation option by default
minor comment cleanup.
update readme for sticky nav notice