[renderjson.js] Return the renderjson object in set_icons() so we can chain things.
[renderjson.js] Add option to show everything by default.

Closes #1
[README.md] Add paragraph about lazy rendering.
[README.md] Let github syntax highlight the example html.
[README.md] Document the 2 options we have (set_icons() and set_show_by_default()).
[test.html] Add our options for testing (commented out).