Add some type of Resource conversion

As we get higher up in levels it would be nice to have a buildable we can place that converts one resource to another.

Either some type of magic alter or maybe a “caravan” type deal that simple adds a stand that we can attach a thrall to.

Then for example, we simply put in 2 stone and can get 1 wood back and vice versa, and maybe have different conversion rates for different resources such as 2 coal for 1 iron / 2 iron for 1 coal similar to the wood and stone but perhaps 10 stone for 1 iron and so one… however you wanted to make the conversion process but have something available once a little higher level is reached.