Include yard-based density units

[aharres]

It would be nice to have yard-based density units like DensityUnit.PoundPerCubicYard.

[angularsen]

Sounds reasonable to add. If you are willing to attempt a pull request, detailed steps are here:
https://github.com/angularsen/UnitsNet/wiki/Adding-a-New-Unit

[aharres]

I created a pull request here: https://github.com/angularsen/UnitsNet/pull/1334

[angularsen]

Merged #1334

[aharres]

Awesome! Thanks.