Added codes on finding duplicates in row/column/3x3 box.
Made difficulty modes to public such that others can use them without
the need of recreating them in their own classes.
Made 2 lists of integers to keep track of the numbers that have tried
and numbers that are available for backtracking.
Modified code to use the tracking lists of numbers. Still haven't
implement backtracking.
Have backtracking working. An IllegalArgumentException occurs most of
the time. Sometimes it get passed and produce the sudoku.
Commit from Richard.
Changed Hint System a bit
Merge pull request #3 from wynestic/master

Changed hintsystem a bit
Hint System
Merge pull request #4 from wynestic/master

Hint System
Added debug loggings. Try to create a LegalCheck class for Sam and
Richard to use.
Merge branch 'master' of ssh://git@github.com/sphan/COMP2911-Project.git

Conflicts:
	Project/src/HintSystem.java
Unit class
Merge pull request #6 from wynestic/master

Unit class
Generate full board with no problems. Need to implement uniqueness tests
when removing cells.
LegalCheck is now work and running.
Added a few functions due to the creation of LegalCheck.java.
A full puzzle can now generate without problems using LegalCheck.java.
Small changes to main due to changes in the Puzzle class.
Small changes.