https://github.com/libgdx/libgdx/wiki/External-tutorials
http://tutorials.boondog.xyz/
https://www.udemy.com/master-libgdx-java-game-development-and-beyond-volume-one/
https://www.quora.com/What-are-some-of-best-libgdx-tutorials-online
http://williammora.com/a-running-game-with-libgdx-part-1
http://steigert.blogspot.gr/2012/02/1-libgdx-tutorial-introduction.html
http://libgdx.badlogicgames.com/documentation.html
https://libgdx.badlogicgames.com/index.html
http://www.kilobolt.com/day-1-flappy-bird—an-in-depth-analysis.html
http://www.gamefromscratch.com/page/LibGDX-Tutorial-series.aspx
https://www.codeandweb.com/texturepacker/tutorials/libgdx-physics
https://github.com/libgdx/libgdx/wiki/A-simple-game