* propname name of new property
* propvalue value of new property
*/
-void vcard_add_prop(struct vCard *v, char *propname, char *propvalue) {
+void vcard_add_prop(struct vCard *v, const char *propname, const char *propvalue) {
++v->numprops;
v->prop = realloc(v->prop,
(v->numprops * sizeof(struct vCardProp)) );