Create custom snapshot renderer

[JakeSidSmith]

This should stub the CanvasRenderingContext2D and create an ascii representation that is written to a file to check for changes later.

expect(context).toMatchCanvasSnapshot();

expect.extend({
  toMatchCanvasSnapshot(received, argument) {
    const pass = //;

    if (pass) {
      return {
        message: () => `expected ${received} not to match snapshot ${snapshot}`,
        pass: true,
      };
    } else {
      return {
        message: () => `expected ${received} to match snapshot ${snapshot}`,
        pass: false,
      };
    }
  }
});