We really need functionality like this when memory maps aren't suitable,
either because they're too slow or because they just aren't available (like
for reading stdin). However, this particular approach was completely bunk.
Namely, the interface was all wrong. The caller needs to maintain some kind
of control over the search buffers for special output features (like
contexts or inverted matching), but this interface as written doesn't
support that kind of pattern at all.
So... back to the drawing board.
