backport ZettelBacklinks as VimwikiGenerateBacklinks

[MartyLake]

Some vimwiki commands have Generate versions:

• VimwikiDiaryGenerateLinks
• VimwikiGenerateLinks
• VimwikiGenerateTagLinks

But some dont:

• VimwikiBacklinks

I found this extension providing the command ZettelBacklinks https://github.com/michal-h21/vim-zettel/blob/c0230fb9f3d0f4aa10c6598549a733e20eeaa92f/doc/zettel.txt#L173-L175 , which should really be VimwikiGenerateBacklinks following the existing convention.

Maybe it should be backported to vimwiki vanilla ?

If doing so, beware of including that patch michal-h21/vim-zettel#149

EDIT: patch was merged upstream

[brennen]

Asked @MartyLake to write this one up after some IRC discussion. Seems like a fine idea.

(This may be a duplicate issue, but we haven't found the other one yet if so.)