Merge pull request #201 from niksoper/gh-pages-dev

Removed reference to missing closeBtn.gif
Merge branch 'upstream' into gh-pages-dev
Update "Did You Know?"

Explicitly references the App Store in the descriptive text
Merge pull request #202 from tpkelly/gh-pages-dev

Update "Did you know?"
Update dist/

Imports the latest develop distribution into the website.
Mostly just docs changes, to include the DateFrequency docs.
Merge pull request #203 from tpkelly/gh-pages-dev

Update dist/
Using cdnjs links for d3 and crossfilter