VERSION 0.100.928: support for custom (code) variations — JWildfireSwan Steam update #3725996

I now added support for custom variations (in glsl shader language), which are compiled on GPU. While they are different from JWildfire custom variations (which are written in Java code) it is also very straight-forward to create them (at least for more simple variations). To help with this, several examples are provided (via variation presets) and there is a dedicated editor-window which shows syntax/compile errors on the fly. To make the custom variation code more easy to handle, it contains several sections all into one file: parameter definitions, the actual glsl code, custom functions etc. There is also a comprehensive manual entry about creating custom variations. Complete changelog: - added support for custom code in the render pipeline - created a custom code editor-window - new application signals to show compile- or parse errors from the render pipeline - added a "custom_glsl_c...