First part of the new API

- Adds the perlin and brownian functions for the new API.
- Also supporting types: Point2d/3d/4d and Seed.
- Adds new examples, which use Image to generate PNGs.
- Update the README.md to offer basic reference documentation of the new API.
- Remove the fastest quality setting, as it didn't produce usable results. What used to be "Standard" is now "Fast".

Note that the old API remains largely intact. The only meaningful change to it is the quality settings.
Could you use fences and specify the syntax?

    ~~~rust
    blah
    ~~~