Add SVG options to render using paths.

[whomwah]

This continues the great work of @HuBandiT in rendering SVGs using a single <path> node. This greatly reduces complexity and size. The example SVG in the specs goes from 27K down to 1.8K (~1400% smaller).

It goes down to 1920 bytes on the same test (uncompressed; gzip-compressed it is down to 711 bytes).
Plus quality is better too, since we are no longer packing individual rectangles (squares) next to each other, hoping rounding is correct everywhere downstream (rasteriser, or conversion to other vector formats e.g. PDF) so that no white lines occur between them (did happen to me a few times). (Plus since it's a single object, I have a hunch it processes/displays/edits faster downstream too.)

but makes makes it opt in for the time being using:

RQRCode::QRCode.new("https://kyan.com").as_svg(
  use_path: true
)

example_output => <path d="M0 0h7v7h-7zM8 0h7v2h-1v1h1v1h-2v-2h-1v-1h-2v2h-2v-1h1v-1h-1zM17 0....h3v3h-3zM17 24v1h1v-1zM21 1h1v1h-3zM9 27h1v1h-1zM26 27h1v1h-1zM28 27h1v1h-1z" style="fill:#000" transform="translate(0,0) scale(11)"/>

This means we keep the backward compatibility, but give users the chance to opt-in. Opting in should show no change to the outputted QR Code and only change the markup.

In a future version of this Gem, this option will be made default after a bit more testing in the field.