[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/include/common/vector.h

@@ -31,9 +31,14 @@ typedef struct Vector
 }
 Vector;
 
-Vector * vector_create(size_t itemSize, size_t capacity);
+// Dynamically allocates the vector
+Vector * vector_alloc(size_t itemSize, size_t capacity);
 void vector_free(Vector * vector);
 
+// Uses existing vector, but dynamically allocates storage
+bool vector_create(Vector * vector, size_t itemSize, size_t capacity);
+void vector_destroy(Vector * vector);
+
 inline static size_t vector_size(Vector * vector)
 {
   return vector->size;