Copy data into a stralloc
#include <stralloc.h>
int stralloc_copy(stralloc* sato,stralloc* safrom);
stralloc_copy copies the string stored in safrom into sa. It is the same as stralloc_copyb(&sato, safrom.s, safrom.len). safrom must already be allocated.
The data that sa previously contained is overwritten and truncated.
If stralloc_copy has trouble allocating memory, it returns 0. Otherwise it returns 1.
1 for success, 0 on memory allocation failure.