Working version of first example from Chapter 12 for Linux

[cortical_iv]

I just spent about a week on this, so put it up at github:

https://github.com/cortical-iv/hello_fltk

It works on my Ubuntu 16 machine using g++ 8.1 with  fltk version 1.4. I did this because I noticed so much of the stuff online was for people using Windows in particular Visual Studio. I am using Qt Creator, which uses cmake, so really wanted to get it working using cmake. You will find the CMakeLists.txt file in the project.

This took me about two weeks learning about makefiles, cmake, and hitting my head against the wall.

It incorporates the debugging from this thread:   

https://groups.google.com/forum/#!msg/ppp-public/BtlzdWGuQpQ/KuDN4u-SPKgJ

I also got a ton of help getting the cmake build to work from the kind folks at fltk.general: 

https://groups.google.com/forum/#!topic/fltkgeneral/LW7xOP4lb8g   

Please ignore that thread, though, as it shows how embarrassingly little knowledge I have of cmake.

The one take-home message for me: external libraries are hell and you basically just have to pray that the ones you depend on have saints in charge, like the good folks who build and maintain FLTK.