openreadclose - read a whole file into a stralloc
(const char *filename
openreadclose opens the file filename
for reading and reads the whole
content into the stralloc sa
. The file is read in chunks of
bytes size. If everything worked fine, openreadclose returns 1.
If the file did not exist, openreadclose returns 0. On every other error,
openreadclose returns -1 and sets errno appropriately.