More unit tests!

[shawnbot]

The d3-specific and purely visual test doc is no longer sufficient. We need a real unit tests that run in IE8 (maybe QUnit?).

[shawnbot]

Most of the work here has been done in #47. See that PR for testing instructions.

The current test runner is QUnit, but we don't have D3-specific tests yet. The current suite cursorily tests a small subset of ES5 features and DOM APIs that are notably in both IE8 and IE9's implementations.

[shawnbot]

Some more tests to include:

• test classList shim on SVG elements (see: IE9: classList shim fails on SVG elements WebReflection/dom4#10)
• events: at the very least, we should check that HTML elements have the right W3C Event methods
• better coverage of CSS properties (see: Additional work on CSSStyleDeclaration #17)