Switched to CMake structure.

[erikdattilo]

To support different IDE and compilers I prepared a CMake (https://www.cmake.org/) project. It may potentially support other OS (e.g. linux) also, but in such case it should be tested.

I appreciated your extensive usage of comments, so I tried to do the same in two ways:

• complete comments on CMakeLists.txt file
• updated Readme.md with instructions about usage

The list of changes is as follows:

• Added CMakeLists.txt file (check it, it should be self-explanatory)
• Added .gitignore to ignore cmake/vs generated files
• I don't have glut installed on my system, so I added a way to easily compile and use it through CMake.
• I deleted the VC/ folder, since with CMake project/solution files are automatically generated.
• graphics.c : solved a compilation error on VS2019
• matlib.h/.c: I had a compilation error. I did a quick&dirty fix. I'd like if you could suggest a better way to fix it (possibly reverting to C function overloading).
• simlib.c: Changed to reflect changes on matlib.h/.c That's all.

To test it: I suggest to download this branch in an empty folder and follow instructions from the Readme. In this way you can also validate the instructions themselves.