New features

• Support for includes in shaders.
  For now it only works with the Lygia library, which can be installed from the package manager.
  See the tutorial: https://vimeo.com/583311513

Improvements

• Time bar will be much more fluid and precise
• OpenGL for the UI has been enabled on windows as it seems to work correctly by default.
  On Mac it is OTOH much laggier than software rendering so it is disabled.
• Fix that one could do save / save as / ... when a document wasn't open, leading to a crash (thanks JM Colin!)
• Fix syntax coloration which had been broken semi-recently ; fix an issue with live-editing JS scripts.