feat(stack): introduce a stack ds, internally this uses a sll

test.c

@@ -1,3 +1,4 @@
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -76,4 +77,25 @@ main(int argc, char *argv[])
 
     free(a);
   );
+
+  test("stack",
+    char *a = "a";
+    char *b = "b";
+    char *c = "c";
+
+    ds_stack_t *stack = ds_stack_init();
+    it("pushes an item", ds_stack_push(stack, a) == 0);
+    it("pops an item", ds_stack_pop(stack) == a);
+
+    ds_stack_push(stack, b);
+    ds_stack_push(stack, c);
+
+    it("peeks ahead", ds_stack_peek(stack, 0) == c);
+    it("peeks past the stack", ds_stack_peek(stack, INT_MAX) == NULL);
+
+    ds_stack_pop(stack);
+    ds_stack_pop(stack);
+
+    free(stack);
+  );
 }