Use childNodes rather than getElementsByTagName.

getElementsByTagName() returns all descendants, which means it iterates
over children of things you have already discounted. childNodes returns
only the immediate children.
Use scrollIntoView to move to element.
Merge pull request #1 from dracos/use-childNodes

Use childNodes rather than getElementsByTagName.
Merge pull request #2 from dracos/scrollintoview

Use scrollIntoView to move to element.
Update Chrome extension
Update Chrome extension

Only return element nodes