Fixed line buffering bug in Stdio.FILE()->getchar().

{n,}gets() now support ignoring partial lines at EOF.
Added tc{get,set}attr() as optional members of Stdio.Stream.
Added constants TCSA{NOW,DRAIN,FLUSH} for convenience.
Made set_{read,write}_oob_callback() optional members of Stdio.NonblockingStream.
Added some Autodoc mk II markup.

Rev: lib/modules/Stdio.pmod/module.pmod:1.246