New lookup feature

[Russ Cox]

> I would have a wish.
>
> As one of the original purposes of the OEIS
> was to find references for articles and books
> dealing with a sequence, could we have a way to
> ask for entries with at least one published  REF ?
>
> Perhaps we could have an extension of the syntax
> where Ref:  (without anything or with spaces after
> the ':')  means  "check for at least one such non-empty line".

This syntax works now.

Russ