v0.6 Almost ready for sorting algorithm implementation

Still TODO:

• make test for signs (- +)
• make test for non-numbers input
• make test for empty list
• make test for a list with '0'
• make test to swap a list with two and three numbers
• make test to swap a list with four and five numbers

Adding more tests at MU_TEST_SUITE:

Most difficult test to build, until now: test_buildstack_argv

How to simulate argvs from user? How to translate this data?
Besides everything is a number on a computer, the terminal treats user's input as strings, even it looks like a number ;)
So, how about calling the split() to cut user input at every space?

Updating Makefile to simulate user numbers input for ./push_swap <numbers>

Full Changelog: v0.5...v0.6