Implemented Hilbert in 2d

Copied most of `canvas_lines_colors.html` for a base to show the 2d Hilbert Curve.
Saved `hilbert2D.js` to both `src/extras/geometries/hilbert2D.js` and `examples/js/geometries/hilbert2D.js`

P.S. Any thought on where Hilbert3D should go?, I don't think it exists as a standalone file.