Add correct code examples

BCB/Popescu et al/ex01.c

+unsigned fun1(unsigned x) {
+   unsigned t = 0;
+   if (x < N) {
+     t = b[a[x] * 512];}
+   return t;
+}

BCB/Popescu et al/ex01_secure.c

+unsigned fun2(unsigned x) {
+   unsigned t = 0;
+   if (x < N) {
+      _mm_lfence();
+      t = b[a[x] * 512];}
+   return t; 
+}

BCB/Popescu et al/ex01_secure2.c

+unsigned fun3(unsigned x) {
+   unsigned t = 0; 
+   if (x < N) {
+      unsigned v = a[x];
+      _mm_lfence();
+      t = b[v * 512];}
+   return t;
+}

BCB/Popescu et al/ex_cond.c

+unsigned fun4(unsigned x) {
+   unsigned t = 0;
+   if (x < N) {
+      unsigned v = a[0];
+      t = b[v * 512];}
+   return t;
+}