Pyshader

* We renamed from python-shader to pyshader!
* Added support for control flow: if-statements, ternary operations, for-loops and while-loops.
* Added support for extension instruction sets (loads of common math/shader functions, like `sin()`, `distance()`, et.c
* Several other smaller improvements along the way.

Fixes for uniforms and descriptor sets.

Some bug fixes, and de-duplication of texture type definitions in SpirV output.

Quite a bit of work overall. Most notable is the added support for textures.

First release. Very much a wip, but we need it for wgpy-py.