Refine coal (later petrogas, solid fuel, rocket fuel and nuclear fuel) to drone fuel to be used with Transport Drones.

Moves the tech requirements for drones to the start of the tech tree to get started quicker.

Support for:
+ https://mods.factorio.com/mod/bobelectronics (uses basic circuit board)
+ https://mods.factorio.com/mod/pyhightech (uses simple circuit boards)
+ https://mods.factorio.com/mod/pypetroleumhandling (uses small parts in recipes)
+ https://mods.factorio.com/mod/aai-industry (replaces drone-engine-unit with electric-motor. adds processed fuel to drone fuel)
+ https://mods.factorio.com/mod/Krastorio2 (Vehicle fuels to drone fuel)
+ https://mods.factorio.com/mod/bobplates (Enriched fuel to drone fuel)
+ https://mods.factorio.com/mod/angelsindustries (Plutonium nuclear fuel and Fusion nuclear fuel to drone fuel)
+ supports hydrogen to drone fuel. (Any mod that adds a hydrogen fluid with a fuel value should be supported)
+ supports natural gas (from various mods) to drone fuel

original work done by tubs (https://mods.factorio.com/mod/Transport_Drones_Fuel).