Nesting

This includes #2.

New from #2: move helper functions out of jsml.dom, support deep nesting in Arrays: `["ul", [$("<li>1</li>"), $("<li>2</li>"), $("<li>3</li>"), [$("<li>4</li>"), $("<li>5</li>"), $("<li>6</li>"), [$("<li>7</li>"), $("<li>8</li>"), $("<li>9</li>")]]]]`.

Not sure if this (deep nesting) is actually needed, but this change makes the code a bit cleaner and removes copy-pasted parts.

One more change: a `hasOwnProperty()` check was added to the `for … in …` loop.