Append a character to a stralloc
#include <stralloc.h>
int stralloc_append(stralloc* sa,const char* in);
stralloc_append appends the byte from *buf to the string stored in sa, allocating space if necessary, and returns 1.
If it runs out of memory, stralloc_append leaves sa alone and returns 0.
1 for success, 0 on memory allocation failure.