Add timer.c for measuring labtime.

+#include <stdio.h>

+#include <timer.h>
+
+long tic(void){
+    struct timespec time_spec;
+    clock_gettime(CLOCK_THREAD_CPUTIME_ID,&time_spec);
+    return time_spec.tv_nsec;
+}
+
+long toc(long prev){
+    struct timespec time_spec;
+    int now;
+    
+    now = clock_gettime(CLOCK_THREAD_CPUTIME_ID,&time_spec);
+    return time_speck.tv_nsec - prev;
+}
+