[common] vector: eliminate double allocation when possible

This commit creates two constructor/destructor pairs for vector:
* vector_alloc/vector_free dynamically allocates the vector itself
* vector_create/vector_destroy uses existing Vector objects

common/src/vector.c

@@ -25,22 +25,16 @@
 #include <stdlib.h>
 #include <string.h>
 
-Vector * vector_create(size_t itemSize, size_t capacity)
+Vector * vector_alloc(size_t itemSize, size_t capacity)
 {
-  Vector * vector = calloc(1, sizeof(Vector));
+  Vector * vector = malloc(sizeof(Vector));
   if (!vector)
     return NULL;
 
-  vector->itemSize = itemSize;
-  vector->capacity = capacity;
-  if (capacity)
+  if (!vector_create(vector, itemSize, capacity))
   {
-    vector->data = malloc(itemSize * capacity);
-    if (!vector->data)
-    {
-      free(vector);
-      return NULL;
-    }
+    free(vector);
+    return NULL;
   }
   return vector;
 }
@@ -49,10 +43,33 @@ void vector_free(Vector * vector)
 {
   if (!vector)
     return;
-  free(vector->data);
+  vector_destroy(vector);
   free(vector);
 }
 
+bool vector_create(Vector * vector, size_t itemSize, size_t capacity)
+{
+  vector->itemSize = itemSize;
+  vector->capacity = capacity;
+  vector->size     = 0;
+  vector->data     = NULL;
+
+  if (capacity)
+  {
+    vector->data = malloc(itemSize * capacity);
+    if (!vector->data)
+      return false;
+  }
+  return true;
+}
+
+void vector_destroy(Vector * vector)
+{
+  free(vector->data);
+  vector->capacity = 0;
+  vector->itemSize = 0;
+}
+
 void * vector_push(Vector * vector, void * item)
 {
   if (vector->size >= vector->capacity)