if=... tests

I added some tests for `if=...` in templates.   They are failing, either due to bugs in my tests, in your code, or both.   Or my misunderstanding about the spec for `if=...`.

I more-or-less copied the format of your existing tests, except for calling `test.async()` which seems useless to me.

I'm actually unclear why your tests insert a `<template>` tag into the document and then expect the contents of the `<template>` tag to change based on binding.   The purpose of a template is to be a blueprint used to create "instances", and then those instances are bound to conditions.

I'm also unhappy about this [BDD library](http://chaijs.com/api/bdd/).   It's clever how they make the code look like English, but AFAICT there's no easy way to tell which assert failed, assuming that you do two tests for the same value, ex:

```
expect(foo).to.equal(2);
expect(bar).to.equal(2);
```

Note that the other project (at least the ones I know about) are just using chai/assert.