Added common include for simple C programs, and threads-intro code

threads-intro/t0.c

@@ -0,0 +1,28 @@
+#include "common.h"
+#include "common_threads.h"
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+void *mythread(void *arg) {
+    printf("%s\n", (char *) arg);
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {                    
+    if (argc != 1) {
+	fprintf(stderr, "usage: main\n");
+	exit(1);
+    }
+
+    pthread_t p1, p2;
+    printf("main: begin\n");
+    Pthread_create(&p1, NULL, mythread, "A"); 
+    Pthread_create(&p2, NULL, mythread, "B");
+    // join waits for the threads to finish
+    Pthread_join(p1, NULL); 
+    Pthread_join(p2, NULL); 
+    printf("main: end\n");
+    return 0;
+}
+