try a new approach for generator/resolver
try different approach for generation

unfortunately, it fails
last commit before branch and rewrite
rewrite much, delete class field, change algorithm

* algorithm changed to recursive version,
	backtracking should now be more manageabla
* class field not necessary anymore
	working with a grid of integers instead
added print statement to track progress
tried something
fix for loop in getCandidates

loop head was defective
counter variable was running from 0 to 8
when it should have been running from 1 to 9
resolve() now correctly solves an empty sudoku

yeeee-haawwww!!!
fix potential memory leak, allow loading sudokus

* update README.md
* add comment to test.cpp explaining its purpose
* add loadArray() to sudoku.cpp which allows loading an existing sudoku
  as an array of ints
* add constructor taking an existing sudoku as an array of ints
* delete the allocated candidate lists in resolve() to avoid a memory leak
make generate() work

crude draft of the method, has bug:
	if the 3x3 block beginning at (6,6) is populated, the algorithm
	will take awfully long to resolve the sudoku
commented out useless attribute

"bool writable[9][9]" was never useful
therefore commented out
fix nasty generation bug

now, generate() will never populate the 3x3 block starting at (6,6)
before calling resolve(), because if it did
resolve would go totally crazy and run for a very long time
(I have never found out how long. Normally, on my machine,
total run time of the test program is a few milliseconds.
When resolve() goes crazy, it spun around for minutes without a result
so I always killed it.)
small refactor