Use designated initializer more

Designated initializers are supported in C99 and simplify struct
initializations.  All members not explicitly mentioned are default
initialized to 0, and also modern compilers can warn on of those missing
ones.

Hashtable.c

@@ -109,13 +109,15 @@ static size_t nextPrime(size_t n) {
 }
 
 Hashtable* Hashtable_new(size_t size, bool owner) {
-   Hashtable* this;
-
-   this = xMalloc(sizeof(Hashtable));
-   this->items = 0;
-   this->size = size ? nextPrime(size) : 13;
-   this->buckets = (HashtableItem*) xCalloc(this->size, sizeof(HashtableItem));
-   this->owner = owner;
+   size = size ? nextPrime(size) : 13;
+
+   Hashtable* this = xMalloc(sizeof(Hashtable));
+   *this = (Hashtable) {
+      .items = 0,
+      .size = size,
+      .buckets = xCalloc(size, sizeof(HashtableItem)),
+      .owner = owner,
+   };
 
    assert(Hashtable_isConsistent(this));
    return this;

Vector.c

@@ -25,14 +25,16 @@ Vector* Vector_new(const ObjectClass* type, bool owner, int size) {
 
    assert(size > 0);
    this = xMalloc(sizeof(Vector));
-   this->growthRate = size;
-   this->array = (Object**) xCalloc(size, sizeof(Object*));
-   this->arraySize = size;
-   this->items = 0;
-   this->type = type;
-   this->owner = owner;
-   this->dirty_index = -1;
-   this->dirty_count = 0;
+   *this = (Vector) {
+      .growthRate = size,
+      .array = xCalloc(size, sizeof(Object*)),
+      .arraySize = size,
+      .items = 0,
+      .type = type,
+      .owner = owner,
+      .dirty_index = -1,
+      .dirty_count = 0,
+   };
    return this;
 }