Save named, location and quickfix lists, viminfo alike

[ntnn]

A neat feature would be to save the named lists as well as the
location/quickfix lists like a viminfo file.

For qf/named it's relatively easy, qf is global and named already have
their identifiers.

[quickfix]: {...}
named list 1: {...}
named list 2: {...}

Saving the file like this would make it relatively easy to reparse it,
using json_encode and json_decode to transform the lists.

For location lists, it might be sufficient to save those with their
referring filenames and an incrementing number, but that's still not
a very nice solution.

Or those could just be dropped and only the named (and maybe qf) lists
are saved.

Also this feature would primarily be usefule on a per-project basis, so
the files would need to be created in a separate folder with an
identifiable name, like vim-gutentags does it for tags.

[romainl]

If people had ! in their viminfo option, we could simply have QF_QF_LIST, QF_LOC_LIST_FILENAME, QF_NAMED_LIST_LISTNAME, etc. saved directly and automatically in ~/.viminfo. I don't think it would be wise to force that option on the user, though.

Saving and restoring lists to/from a file will add a lot of complexity to the plugin. I'm not sure that's something I want but the idea is certainly interesting.

[ntnn]

Well, that could be mentioned in the docs - if a user would like to use
the functionality they'll have to add it.

Complexity is a fair point, especially the detection of the base
directory would duplicate lots of code already present in other plugins,
as well as loading/saving per-project.

While the addition would be appreciable I'm not sure if the work would
measure up to the usefull-ness.

I think it'd be more helpful to have auto-filled named lists, but thats
easily done with a function.