Move context-specific callout to general tag usage
Move button-tags section to start of button section
upgrade OS X tests to Yosemite

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Merge pull request #15149 from twbs/yosemite

upgrade OS X tests to Yosemite
upgrade iOS tests to 8.1

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Merge pull request #15150 from twbs/ios-8.1

upgrade iOS tests to 8.1
Add modal autofocus example
Merge pull request #15135 from hillai/patch-1

Add modal autofocus example
Merge pull request #15139 from patrickhlauke/docs-button-section-restructure

Docs button section restructure
rm redundant role="button" from <button>