[Therion] Breaking a loop at a specific station on extended elevation

[Tarquin Wilton-Jones]

> This would make an excellent mini topic on the wiki (in the existing
> article on "extend").


I have now added a new article, with details of the investigation:
https://therion.speleo.sk/wiki/breakingextend

Because it uses a load of images, it was nicer to have it as a separate
article, rather than litter the existing one. Bruce, please double check
you are happy with how I linked it from your "extend" article.