#562 - Removes the heading
#562 - Makes the UX and Workflow at equal levels
#562 - tightening up the copy for ux and workflow
#562 - fixing styles to be more responsive
Fix a KeyError when there's no User-Agent header field 

I happened to find 500 errors for requests without the User-Agent header field. I apologize that I have not tested this code. I'd appreciate it if anyone could run a test before merging. Thanks.
Adding Twitter Cards, OGP
Twitter Cards, OGP only on tutorials
Merge remote-tracking branch 'upstream/master' into semantics
reverted share image change
Fixes #576
Merge pull request #577 from ebidel/cssbgchange

Fixes #576
Merge pull request #574 from tmatsuo/patch-1

Fix a KeyError when there's no User-Agent header field
Merge pull request #575 from agektmr/semantics

Adds social media sharing meta tags for Twitter Cards, OGP
Merge pull request #572 from PaulKinlan/mobile_updates

Cleans up the Mobile Landing page - Fixes #562 LGTM
Fixes #586 - url for image in the twitter card
Fixes #586 - url for image in the twitter card and fb