Add support for RPi RGB LED Matrix displays

[chrisys]

@rm-hull I have been using luma.oled for some time on my train departure display project. Recently someone asked if I could add support for larger LED matrix panels.

I'd worked with this library before: https://github.com/hzeller/rpi-rgb-led-matrix

Not wanting to completely rewrite my project to support a different library, I went about looking to see if I could connect it with luma.led_matrix. It turned out to be pretty straightforward and works exactly as I'd hoped.

Before doing any further work on this though I wanted to get your guidance on contributing this functionality, and if it's even desirable for the project.

[rm-hull]

Excellent work! The class you wrote is just a simple bridge/adapter between the two implementations and is how I would’ve tackled it too. I like the fact you import inside the class, but it might be worth catching ImportError and then printing a useful message indicating that an external dependency needs installing.

as to whether it should be included in this project .. it would need some documentation and tests if we want to include it. Presumably it doesn’t need to be declared inside the project for it to work? Personally though I’d be happy to accept it - what do you think @thijstriemstra ?

[thijstriemstra]

+1!

[chrisys]

OK cool, since you guys are on board I will develop it more, add documentation and look at adding tests too (although I may need some guidance here, but I'll take a look and come back if I have any specific questions).

[thijstriemstra]

any news @chrisys?

[chrisys]

Sorry guys some stuff came up; I still have all the hardware for this and do intend to get back to it one day!