Make sz_malloc/free use the default allocator when no allocator is provided.
Fix formatting of sz_get_error decl.
Add missing sz_set_stream.
Remove null allocator checks now that sz_malloc/free handle it.
Clarify reader remarks.
Note on the pointer returned by sz_stream_null.
Write docs for sz_stream_eof and sz_stream_close.
Fix incorrect mode check in sz_bufstream_write.

Was causing a failure in a test.
Fix return value of sz_fstream_read and _write.

Because fread/write returns the number of objects read, and fstreams try to
write the entire thing at once, only one or zero is returned. As such, it's
necessary to multiply the result by the number of bytes written.
Fix null chunk test in read_compound.
Fix test for unpacked-ness.

The original test for whether something was unpacked was whether it was NULL.
Since porting snowball from snow-palm to a library, though, I just went ahead
and added an unpacked flag so NULL values are permissible.
Add missing whitespace to an else-if
Fix SZ_AS_READER

Was trying to grab a writer because copy/paste problems are fun.
Fix up relative compound offsets. No longer relative to the start of the file.

This was annoying while reading snowballs, so I decided it's better to just use
an offset relative to the compound table.