Housekeeping and code cleaning

[sezna]

entity.rs needs a refactor. The branching on the right and the left is no bueno. Some alternatives:

• Keep the node structure but make a function do the stuff that's duplicated. Thread-spawn it (bench this) on big recursive calls and do both sides at once.
• Change left, right to [Node; 2]
• Node could be an enum of leaf or internal, getting rid of some options
• The tree should be an iter so we don't have to process the entire vec beforehand
• There might be better (unsafe?) ways to represent the tree in memory...maybe.