OpenGL ES 3.2 bindings

This project aims at providing a portable way to write OpenGL (more preciselyOpenGL ES) application in OCaml. It comes in three parts: Low level bindings allowing direct calls to OpenGL ES functions. Thesebindings try to remain reasonably type-safe using polymorphic variantsto encode enumeration types. The low level bindings also provide somesanity checks for the size of bigarrays which allow to capture quite alot of errors with clear messages. High level bindings providing auxiliary functions like matrix inversionto ease the development. For instance, to use shaders with the highlevel bindings, you may use compile_shader with the sources code, toget a value of type unit program. Then, you can set the variables ofthe shaders (uniform or attributes), either as constant or function andget an OCaml function to finally run the shaders.* A wrapper to open a window, start the main loop and interact. Currentlyonly EGL under X11 is supported, but we would like to support differentplatforms in the future (Windows, Android, iOS, Wayland, ...) withoutchanging the interface.