Kaiju Engine (issue #37) - Hook up GL calls to main go thread

Making the setup of a window broken up into 3 phases. (1) Create the window, (2) create the context in go, (3) start the main window event loop. This uses the shared memory to facilitate the stages between C and Go. It's not completely ideal, but it is functional and not too much of a change from the initial implementation. I also moved the glad and GL specific code into the gl package (folder) in the project. Extra helper methods for knowing the state and setting a fatal have been added to shared memory. I also added a wait on the Expose event in x11 as it requires the drawing to happen during that event and not after it.

https://github.com/KaijuEngine/kaiju/pull/38