test: move all module tests to the test/ directory

test/ds/simple.c

@@ -0,0 +1,11 @@
+#include <blue/ds/string.h>
+
+int main(void)
+{
+	b_string *string = B_CSTR("Hello, world!");
+	printf("string object = ");
+	b_object_to_string(string, b_stdout);
+	printf("\n");
+	b_string_unref(string);
+	return 0;
+}