Add IO class
Move specs into unit directory
- prep refactoring prior to introducing functional tests directory
Rename world to grid
- I'm planning to add GameOfLife class which will provide a public interface into the sim.
- the name world is too close to Game Of Life, so I renamed it to minimise ambiguity
- In methods string_to_grid & grid_to_string I replaced the word grid with arr to disambiguate
- from the newly created Grid class
Add GameOfLife class and a functional test
Add runner
Refactor NeighboursCounter
- Remove repetitive code in favour of an iterative structure
- insipred by Greg D's game_of_life_no_return implementation