critical path rendering -> critical rendering path
move images into dedicated folder
sync "object model" content to latest copy
fix collection name
update perf index page
add images for object model content
update 'render tree, layout, paint' content
update render blocking css content
Merge branch 'master' of github.com:PaulKinlan/WebDocs

Conflicts:
	src/site/the-essentials/performance/index.markdown