Merge pull request #834 from jacquerie/master

Fix issue #833
Fixed #819 - added link to media queries doc in performance doc and added periods to TL;DR.
Merge branch 'master' of https://github.com/google/WebFundamentals
Fixed #819 again - tested link live and it wasn't working.
Fix #818 - add link to viewport in performance doc and added periods to TL;DR
Fix sample builder header links
Make iframe scheme relative
Fixed #815 - added periods to TL;DR and to bullet list items.
Merge branch 'master' of https://github.com/google/WebFundamentals
Fixed #814 - lots of small typos fixed