index: simplify examples

The same as:
https://github.com/fsouza/RiverTrail/commit/e0f00feb627d857635f25e46221cf4afbc41c4c1.
Merge pull request #1 from fsouza/master

simplify examples in index page
Add RiverTrail as a submodule.
Get rid of no-longer-needed jslib/ dir.
Pulled down update to RiverTrail submodule.
Include runtimes.js.
Use SSH URL in .gitmodules.