* Avoid initialization order problems [effc++:4].
* Cleaning.
Fix coordinate order when setting up world.
* World: further implement populate().
* Refactoring: make all print function return a string instead of taking a stream.
* Refactoring: make WoodSpecies a class (easier to refactor tmt::find()).
* Refactoring: move config intialization to fixture class in tests.
* Cleaning: add brackets to initialization of object with a Position.
* Fix: LogCapture must be local to tests.
World: complete populate() implementation.