Added space location subgroups for gas giants, asteroid belts, and dw…

[nicholasgower]

…arf planets.

[nicholasgower]

I've added a couple of additional space location sub types to give better support for new types of locations that I have ideas for. The following descriptions of location mechanics are only theoretical at the moment. I've also added documentation for these new sub types.

• Gas Giants: Upon entering a gas giant's orbit, entities called "Gas collectors" are able extract gases from the giant's atmosphere. Gas giants can not be landed on.
• Asteroid belts: Locations that have fly_condition set to true, and serve as a route containing unique asteroids. If any locations are declared as asteroid belts, the Shattered planet will be moved to the asteroid belts subcategory.
• Dwarf planets: Bodies that contain no resources of note, but have exotic surface properties that ensure that certain endgame recipes can only be crafted on a particular dwarf planet.

[danielmartin0]

This is a good blueprint for the future. I think we should monitor what types of planet mods develop to inform our categorization, since there's not much need for this feature to be in place before the planets exist.

[Frontrider]

I support the gas giant, I already have one planned (may not have a full location, that is undecided) and this mod also has one.

https://mods.factorio.com/mod/secretas

I don't know if calling that dwarf planet makes sense.

[bepesStudios]

I am currently making a gas planet mod, would be cool..