feat(lab2): unix lab2 done

Lab 2 is in fact the first lab in the set of ones we actually do. It's
not particularly hard, but consumed some time for me

OSs/lab2/unix/part-A/common.h

@@ -0,0 +1,16 @@
+/*
+ * "THE CHEESE-WARE LICENSE" (Revision 1):
+ * <ElectronixTM> wrote this file. As long as you retain this notice
+ * you can do whatever you want with this stuff. If we meet some day,
+ * and you think this stuff is worth it, you can buy me some cheese
+ * in return
+ */
+
+#ifndef COMMON_H_
+#define COMMON_H_
+
+#define WAIT_FOR_CHILD          0
+#define DONT_WAIT_FOR_CHILD     1
+#define ZOMBIE_PROCESS          2
+
+#endif