Underground heat pipe

once 2.1.x drops do not expect new 2.0.x mods here, mods will be slowly ported based on my needs and/or requests from the community, thx for playing!

This mod took longer than my usual mods since i had to deal with connecting textures, entity build orders & rethink how code structs work.

• yellow, red, blue & green belts are supported (no support for other mods at this time)
• space age is optional, you can use the underground heat pipes anywhere (though the green belts are only loaded with space age present)
• the recipes unlock when you have both the heat pipe and the corresponding underground belt researched
• they can be weaved, not sure why you would, but you can
• the mod uses no on_tick, its all done with hidden entities and listening to just the required events
• in floor heating! tiles between underground are considered warm and toasty
• they are bidirectional, the underground direction indicator is not relevant
• the only difference in tiers is the length they can span, since recipes use heat pipes for the full length try to use the lowest tier
• linked heat pipes when? (or linked connections like the fluidbox has, i mean, the heat prototype also has a connections array)
• no sideloading, direct connections only