Add support for Rembrandt color charts

[dblock]

http://rembrandt.royaltalens.com/en/colourcharts

[thisandagain]

One thing that I'd like to make sure we do when adding color systems (such as this or Winson-Newton) is to ensure that we are "scratching our own itch". While building the Crayola system was super fun, I also had a reason to do it as we were working on a partnership with Crayola at DIY.org at the time. This led me to ensure that I had a simple script that could be used to update the colors and beyond unit testing I actually had a use case to prove it out on.

[dblock]

I was definitely convinced that the Crayola stuff was for fun, how interesting!

I was definitely scratching my own itch when I opened these issues. I was looking for easy tasks for someone learning iOS for some of my own purposes. This library looks great because it's a very straightforward implementation, clear tests and a fun topic. Let me know if you feel strongly about not implementing any of this.

[thisandagain]

Not at all... all for it. 😄 Just want to make sure we are building something maintainable.