Moderngl-window

Improvements

* Optimized the imgui renderer using `ctypes` instead of `numpy` for handling vertex data (aforren1)
* Added support for ALT key modifier in all window backends and other improvements to key handling (OKaluza)
* `WindowConfig` now supports a `fullscreen` attribute

Thanks to Alex Forrence (aforren1) and Owen Kaluza (OKaluza) for the contributions to this release.

New Features

* moderngl and moderngl-window integration for imgui thought the pyimgui project.
This is fairly experimental and the rendered should probably be moved to the pyimgui project soon

> Dear ImGui is a bloat-free graphical user interface library for C++. It outputs optimized vertex buffers that you can render anytime in your 3D-pipeline enabled application. It is fast, portable, renderer agnostic and self-contained (no external dependencies)

* Compute shader support. `WindowConfig.load_compute_shader` and added `compute_shader` parameter for `ProgramDescription`.
* Shaders now support `include` up to a maximum of 100 levels
* Added support for gif anim. This can be loaded as a `Texture` or `TextureArray`
* Added support for loading cube maps
* `WindowConfig.run()` shortcut
* Each window backend now has a `name` property so the user can easily detect what window type they are given
* `WindowConfig` now as a `vsync` property so the user can easily control this from python code
* Scene: New methods to find materials and node by name

Slightly Breaking Changes

* All windows now use 0 samples (MSAA) by default. The default `samples = 4` caused way too much issues
for people with older integrated gpus and when doing headless rendering when multisampling is not supported.

Bug fixes

* Fixed several issues with glft2 scenes and object orientation
* pyglet window: Fixed incorrect mouse position on retina screens and windows
with pixel ratio > 1.
* sdl2: mouse press/release events was reversed
* pygame2: Fix broken mouse wheel reading
* glfw: Incorrect mapping of BACKSPACE key
* glfw: Fixed an issue not setting vsync properly¨
* headless: We now call `ctx.finish()` in `swap_buffers`
* Shader errors should now report the error line more accurately
* Various typo fixes

Improvements

* Windows now has an `exit_key` property that can be used to change
or disable the exit key. This key is `ESCAPE` by default and can
be disabled by setting the property to `None`. This is useful
for users that don't want the default exit key behavior.
* Log consumed glerrors after context creation as warnings

Bug fixes

* Pyglet mouse coordinates was translated wrong in cases were the
framebuffer size is larger that then window. The mouse position
should always use window coordinates.
* VAOs should now properly support 64 bit floats / dvec
* VAOs should be better at detecting/ignoring built in attributes
* `Camera.look_at` had broken input validation when passing in a vector
* Various typos in docstrings

Resolved an issue with version constraints causing some dependencies to install pre-release versions

* Missing `WindowConfig.close` method and support for close callback for all window types
* Bug: KeyboardCamera's matrix is now always returned as a 32bit floats
* Bug: Projection3D's matrix is now always returned as a 32bit floats
* Example cleanup and improvements

* Bug: An `INVALID_ENUM` glerror triggered after querying context info is now consumed.