Add coccinelle script to remove pointless callocs

scripts/coccinelle/uncalloc.cocci

@@ -0,0 +1,13 @@
+
+@@
+expression a;
+@@
+- tor_calloc(1, a)
++ tor_malloc_zero(a)
+
+@@
+expression a;
+@@
+- tor_calloc(a, 1)
++ tor_malloc_zero(a)
+