Add Android extensions tutorial
Update Samples intro for new Android extensions sample
Merge pull request #110 from crosswalk-project/android-ext-925

Add Android extensions tutorial
Make new APIs directory
Allow traversal to links which open a new window

The previous code was intercepting all link clicks to
external links (with a '#' in them) and passing them to Google
Analytics before setting the href of the window to the original
link href. This meant that any target attribute was being ignored.

Allow the default action to take place (i.e. navigation) instead,
so we can open links in new windows/tabs.
Clean up intro pages for APIs

Make the "APIs" page an introductory page which points to
"Web APIs" and "Embedding API" as separate entries.