Add support for global oplist.

Global oplists are global macro defined as M_OPL_##type

Add support of global oplist for macro M_EACH & M_LET.
Partial fix #9

example/ex-array02.c

@@ -2,11 +2,14 @@
 
 // Let's define an array of 'char *' named 'charp'
 ARRAY_DEF (array_charp, char *)
+// Let's register globaly the oplist of array_charp
+#define M_OPL_array_charp_t() ARRAY_OPLIST(array_charp)
+
 
 int main(void)
 {
-  // Create an array list 'al'
-  M_LET (al, ARRAY_OPLIST(array_charp)) {
+  // Create an array list 'al' of type array_charp_t
+  M_LET (al, array_charp_t) {
     // add elements to the array list
     array_charp_push_back (al,"C");
     array_charp_push_back (al,"A");
@@ -18,7 +21,7 @@ int main(void)
     // Display contents of al
     printf("Original contents of al: ");
     // For each element of the array al
-    for M_EACH(element, al, ARRAY_OPLIST(array_charp)) {
+    for M_EACH(element, al, array_charp_t) {
         printf ("%s ", *element);
     }
     printf("\n");