Add implementation for substraction
Added implementation for multiplication as usual
Add test and implementation for duplication op
Basic check for empty stack

Check stack is not empty before a pop, throw an error otherwise
Merge branch 'tp2' into stack_dup
Add STACK system command
Merge branch 'stack_dup' into tp2

Conflicts:
	lua/forth
Added division
Added test for multiplication and addition in the same operation
Dispatch functions for conditions and comments
Define Forth conditions
Implement missing integer comparison operations
Implement EXIT
Implement VERSION
Revert "Implement EXIT"

This reverts commit 082725c6d1f79db274a50f9966e164e8a6102cf1.
Fixed EXIT command
CREDITS !
Proper credits
Merge branch 'tp4-sogiuser6' into tp4-sogiuser8