General cleanup and documentation fixes

• Update README with more examples and help
• Revert back to lg instead of 1x (see 4de0ad3)
• Properly assign props to component (see b3aee58)

Initial stable release

This release uses standard, non-ES6 JavaScript to ensure things work without a build step. Usage mirrors the Font Awesome class API, but a bit more succinct.

There is a basic test suite to ensure backwards compatibility of the API.