io: added IStreamBase and IStreamSeekable forward declarations.
debug_constraints: added TOGO_CONSTRAIN_INTEGRAL_ARITHMETIC(T); tidy.
utility: added sizeof_empty().
memory_io: added MemoryStream::clear(); updated test; tidy.
object_buffer: new class and interface; added test.
io: added sub doc-groups for memory_io and file_io.
collections: @ingrouped interfaces: array, queue, priority_queue.