Add summit demos.

summit2.html is a two pane demo of rust logo and matrix math.

summit3.html is a three pane demo adding longcat.

summit-fail.html is thw two pane demo with failing page on the right.
auto merge of #1011 : metajack/servo/summit-demos, r=larsbergstrom

summit2.html is a two pane demo of rust logo and matrix math.

summit3.html is a three pane demo adding longcat.

summit-fail.html is thw two pane demo with failing page on the right.