Some of our source files, e.g. `engine.c` or `space.h` are getting a bit out of control. Long files are not bad *per se*, but they make recompiling take longer, and source management a bit more painful (more conflicting edits). For the sake of sanity, we should split up larger files into groups of functions that operate together, e.g. `engine_redistribute.c` should contain the `engine_redistribute` function along with all the mappers and code that is called only from that function itself. Assigning to myself, but I am under no illusions that I will be able to tackle this any time soon.