Pyshader

* Add debug support: line numbers make it all the way into SpirV.
* Errors produced by PyShader give much more feedback about what went wrong and where.
* Can now assign to arrays.
* Fixes a few cases where `break` was broken.
* Other fixes to control flow.
* Fixed that large shader would fail.

* Fix spirv block decoration for storage buffers. This fixes that on some drivers on Linux, shaders with storage buffers did not work.
* Fix usage of GlobalInvocationid in our tests and examples.

* Implement dot product using v1 v2.
* Add vector swizzling coords stpq.

* Decorate ArrayStride for storage buffers
* Fix typo, fixing the matrix_inverse function

* Also support mix() with two vectors mixed using a float.
* Enable setting FragDepth as fragment shader output.
* Implement mod + remainder for both ints and float.
* Implement integer division.
* Implement assignments that use tuple packing / unpacking.
* Refactor to make code related to globals and builtins more stable and scalable.
* Some doc improvements to builtin functions.

* Can not also use `=` instead of `:` for adding shader type info to function arguments. In other words, use default values instead of function annotations. This can fix the problem that PyFlakes/flake8 reports "missing name" errors.
* Fix that when the bytecode is longer than 255 bytes, control flow jumps are reported wrong.