Read a whole file into a stralloc
#include <readclose.h>
int readclose_append(int fd,stralloc* sa,
size_t bufsize);
readclose_append reads the whole content into the stralloc sa, appending it to the existing content. The file is read in chunks of bufsize bytes size. If everything worked fine, readclose_append returns 0. On error, readclose_append returns -1 and sets errno appropriately.