Usage: puissance4 <mode> <row> <col>
    mode  specifies the mode:
        1 = single player game (random),
        2 = single player game (AI),
        3 = two players game
row   specifies the number of rows (>= 4)
col   specifies the number of columns (>= 4)

- Created the search_optimal_action method to avoid duplicated code in
the smart_play method.
- Added a print_help method to help the user when using the program.
- Simplified the main.c file in order to use only one method when
playing instead of three.
- Added some comments.
- Performed various small adjustement for more code clarity.

The program valid each tests, but it need some refactoring to improve
the code quality.

- Improvement of the diagonal check.
- Changed the text displayed to be the same than those in the tests.
- Fixed an unknown char that was displayed at the second game display.

The game now must have arguments in order to be played.

Also fixed the horizontal game check that wasn't working when the row
was completed by the middle.

Also fixed a typo in the readme.

Various changes have been done for better game result verification.

Also added rules in the .gitignore to ignore the generated tests files.

Also added a property GameResult to the puissance structure in order to
save the current state of the game.

Small changes to the print_game and manual play to implement the game
result verification.

The display generated a SIGABRT error after multiple print, because the
display string wasn't cleared.

The manual play doesn't use the program arguments yet.

Moved the testbed folder at root and deleted skeleton_for_students
folder.

Edited the makefile in order to run the tests.

Edited the .gitignore to ignore CLion files.

Also implemented the methods for initialize and destroy the game.