Encapsulated build of gui parts

Build system for DearImGui (with implot) with SDL2 and OpenGL intended as a standalone example.

The library is named dig (DearImGUI)

Instructions

clone the two dependencies into directory

git clone git@github.com:ocornut/imgui.git
git clone git@github.com:epezent/implot.git

Then build in traditional cmake fashion
mkdir build; cd build; cmake ..;
make -jN; make test; make install;

The header file dig should be installed so you can include everything. #include "dig/dig"

link against dig::dig

This just lets you use the regular ImGui calls.