[README.md] Mention "themeable" in description.
[README.md] Add link to the live example (gh-pages).
[renderjson.js] Need to use append() on <pre> in case "json" is an empty array or empty object.
[renderjson.js] Split out empty detection into its own function.
[renderjson.js] Build the tree lazily for massive speedups when there's large amounts of JSON.

We only recurse down the tree when someone clicks a disclosure. This means
we only end up building the DOM tree for the parts someone actually wants to
see, which is a huge win when there's a large amount of json data.
[renderjson.js] Re-indent.
[renderjson.js] Indent slightly less on disclosure lines so the {} and [] line up better.
[renderjson.js] Make the disclosure "icons" configurable.
[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).
[index.html] Put the example back that the automatic github pages rendering removed.
Merge branch 'master' into gh-pages to get the latest version of the script.