Implemented calloc()

src/main/fragment/vwuz1=_deref_pbuz2.asm

@@ -0,0 +1,5 @@
+ldy #0
+lda ({z2}),y
+sta {z1}
+lda #0
+sta {z1}+1

src/main/fragment/vwuz1_le_0_then_la1.asm

@@ -0,0 +1,4 @@
+lda {z1}
+beq {la1}
+lda {z1}+1
+beq {la1}

src/main/kc/stdlib/stdlib.kc

@@ -1,5 +1,7 @@
 // Implementation of functions found int C stdlib.h / stdlib.c
 
+import "string"
+
 // Top of the heap used by malloc()
 unsigned char* HEAP_TOP = 0xa000;
 
@@ -20,6 +22,15 @@ void free(void* ptr) {
     // TODO: So far no support for freeing stuff
 }
 
+// Allocates memory and returns a pointer to it. Sets allocated memory to zero.
+// - nitems − This is the number of elements to be allocated.
+// - size − This is the size of elements.
+void *calloc(size_t nitems, size_t size) {
+    void* mem = malloc(nitems*size);
+    memset(mem, 0, nitems*size);
+    return mem;
+}
+
 // Searches an array of nitems unsigned words, the initial member of which is pointed to by base, for a member that matches the value key.
 // - key - The value to look for
 // - items - Pointer to the start of the array to search in

src/main/kc/stdlib/string.kc

@@ -29,6 +29,7 @@ void* memmove( void* destination, void* source, size_t num ) {
 // Copies the character c (an unsigned char) to the first num characters of the object pointed to by the argument str.
 void *memset(void *str, char c, size_t num) {
     char* end = (char*)str + num;
+    if(num>0)
         for(char* dst = str; dst!=end; dst++)
             *dst = c;
     return str;