Comment logConstruct file.
Modifi examples code to return only formula.

Reason:
- simplicity.
Loosen fil_condition method that one field can have more values.

Reasons:
- formula is too complex.
- corectness is enshured by row, column and square conditions.
Add method for presenting solution of sudoku example and modify current
print method for sudoku.

Reasons:
- Easyer to check,
- easyer to see.
Add basic examples.
Add example of solving sudoku puzzle.
Add test for sat in system tests and enable sudoku tests.