Add QUnit integration

[Turbo87]

Example:

import { module, test } from 'qunit';
import { withChai } from 'ember-cli-chai/qunit';

module('test');

test('it works', withChai(function(expect) {
  expect(5, '5 < 10').to.be.below(10);
}));

Resolves #3

/cc @lolmaus @akatov @mattmcmanus @justin-hackin

[Turbo87]

/cc @trentmwillis