The program can now be executed by command line with the following
syntax :

./stack [array_length] [arguments]

This will sort the values passed as arguments and print them in the
console.

Also uptaded the README file with this new execution.

The program can now sort an array using the two stacks methods.

Also fixed various errors in the test file and is_stack_empty methods.

Also fixed some issues in the test file that were caused by the
initialization of a stack's pointer instead of a normal stack.

Some of the tests need a verification for the asserts.

Also fixed some typos in comments or define.

This include :
- .gitignore
- README
- makefile
- Files (main, test, .c, .h)