Moved reset to Puzzle
Optimized solveBruteForce - no need to take a copy, simply readd head
First attempt to create a Puzzle. Way to slow for real
Removed some dead code
Replaced Set<Integer> by BitSet. Doesn't seem to make a huge 
difference in performance and space usage.

Still requires a couple of clone operations.
Generator for fully filled-out Sudoku.
Fast and simple - cannot generate any possible Sudoku, but should be 
able to generate a lot of different versions.

Now we need an algorithm to remove entries and calculate uniqueness.
Merge branch 'BitSet'

Conflicts:
	Sudoku/src/sudoku/Puzzle.java
	Sudoku/src/sudoku/unit/Unit.java

Now with BitSet instead of Set<Integer>. Seems cleaner
CleanUp imports after refactoring