[Therion] Revisiting Breaking extended elevations on specific stations

[Tarquin Wilton-Jones]

> How about...
> extend ignore 8 7 [ (from) | to ]
> ... since we already use the from and to keywords with respect to stations at each end of a survey leg?

It's all good by me.

The only reason I didn't suggest that keyword is that Therion is
stepping through my loop backwards. So a user might assume that the "to"
station is the "to" station from their data, when actually it is the
"to" station from the "extend ignore" pair.

But as long as people think it is intuitive enough, carry on :)