Air filtering tweaks [CAL] v0.0.2

Adds a new 'Iron-Limestone Filter Media' loose product, produced by mixing 3 iron ore + 1 limestone in the Industrial Mixer to yield 4 units. Useful when you have surplus iron ore and want a cheaper alternative to the vanilla filter media production chain.

Source code notition:

Accesses file system

Reads Python definition of mod recipes and products to be loadable within game.
Loads PNG image files to game textures

Uses reflection by name

Accesses the game asset contents to register or edit current game recipes, research and it's position.