replace LibRocket with RmlUI

[HongPong]

As an experiment I'm trying to replace LibRocket with its successor RmlUI which is actively maintained. I'm a novice at C++ but I got most of the way along I think.

RmlUi documentation: https://mikke89.github.io/RmlUiDoc/index.html

Differences with Librocket API in readme here: https://github.com/mikke89/RmlUi/blob/master/readme.md . I think at least I got the font loading API function updated correctly.

My branch attempt here: https://github.com/HongPong/OpenSkyscraper/tree/rml-ui

I took a shot at replacing Source/Rocket/Renderer.cpp, Renderer.h, SystemInterface.cpp, SystemInterface.h . however I don't have a clue what the "renderer" files should be replaced with, if anything.

Would be curious if someone C++ savvy can look this over. Maybe if librocket gets plucked out this thing can move again?

[ia3crt]

I have been trying to help with the project for a week now, but I am being stopped on my tracks by libRocket. Actually did a try at your branch, to install librml (not on my distro repositories), but I am not advancing at all. Just want to show there is interest on the project, but someone with more skills than I do will need to help...

[HongPong]

Cool to hear - I am also such a novice at this area that I gave up - however I am making my own game from scratch to pick at some of these ideas!