Added testem testing to run tests on all browsers and node environment

Added clear function test. Refactored clear function to not instantiate new Array and delete all collection callbacks. Updated README for running test instructions and contribution instructions.

Forgot to mention, using timoxley's assertion library instead of component's because it has all the default assertions in Node that we know and love like assert.deepEqual.

Might possibly go back to other modules and switch out the component assertion library with timoxley's assertion library if we start using something more extensive than a simple expression assertion.