Add assert.js copied from nada

From:
https://github.com/eric-brechemier/nada

CC0 - No Copyright
https://creativecommons.org/publicdomain/zero/1.0/
Add underscore library for use in unit tests

Project:
https://github.com/documentcloud/underscore

Documentation:
http://underscorejs.org/

License:
MIT
Move assert.js to a subfolder of tests

This is consistent with underscore added as a subfolder of the tests folder.
Remove nada from tests folder

I decided to use QUnit instead in the tests, while including nada
as a submodule for the implementation in code/.
Add nada as a submodule in code/nada

Project:
https://github.com/eric-brechemier/nada

License:
CC0 - No Copyright
Add QUnit as a submodule in tests/qunit

Project:
https://github.com/jquery/qunit

License:
MIT
Use git:// URL for qunit submodule
Add JSON-js as a submodule in tests/json

Project:
https://github.com/douglascrockford/JSON-js

License:
Public Domain
Add HTML page for unit tests using QUnit
Add unit tests for compact()