buffer_fromsa - initialize buffer structure from stralloc

       buffer_fromsa  makes a virtual read buffer from a stralloc.  The buffer reading functions will be able to
       read until the end of the data in the stralloc, then signal EOF.  The buffer does not have its own buffer
       space, it reuses the one in the stralloc.

       Do not touch the stralloc until you are done with the buffer!  In particular, do not  call  stralloc_free
       on it!

       Reading data from the buffer will not change the stralloc.

       buffer_fromsa - initialize buffer structure from stralloc

buffer_tosa(3), buffer_init(3), buffer(3), buffer_frombuf(3), buffer_fromarray(3)

                                                                                                buffer_fromsa(3)

#include<libowfat/buffer.h>

       void buffer_fromsa(buffer* b,const stralloc* sa);