More systematic way for adding assertions

We are looking into brining more assertions into the engine.

Basically we are probably going to have an assert method that checks if a certain condition is being met and throw an error otherwise (basically like `t.ok` in tape). The issue is to make this minifiable/ integrate with our existing tools.

The proposed solution can be found here:
- Browserify transform: https://github.com/alexanderGugel/engine/blob/assert/scripts/optimize-assertions.js
- `assert()`: https://github.com/alexanderGugel/engine/blob/assert/utilities/assert.js
- Sample usage: https://github.com/alexanderGugel/engine/blob/assert/dom-renderers/DOMRenderer.js

Feedback is very welcome. The main goal is to
1. avoid unnecessary function calls (micro optimization - yay!)
2. have the ability to remove error messages for minification purposes.
3. avoid being locked into browserify by adding **optional** transform steps.

@michaelobriena