Add option to prefix links with filename before anchor tag

[dakra]

I use org-make-toc for my Emacs config which is pretty big
and having init.org always display everything on the main github page would
be too heavy. Therefore I just render a README.org with a table of contents that points
to the init.org file.

This PR adds option to prefix the links with the filename so I can
copy&paste it from my init.org to the readme.

I first thought about making it in a way that doesn't involve me
copy and pasting but then figured I don't update the sections that
often and it's a very simple solution.

[alphapapa]

Hi Daniel,

Thanks, that is a very simple solution. However, I think it wouldn't take much to add support for ToCs of contents in other files. Would you prefer that? I think I could add it without much trouble.

[dakra]

@alphapapa I even thought (briefly) about adding another
org property (TOC_DESTINATION? or the other way around
TOC_SOURCE?) but found it not too intuitive.
Then I started just another command org-make-toc-other-file
but saw it's a bit more complicated than I thought and
just went with this very simple approach.

But long story short, yes, I would like very much
if you implement that.
(Also use file-relative-name in case source/destination
is in a different directory? Not sure if that even works
in Github)

Thanks!

[alphapapa]

I think you were right in the first place. I started to work on the idea and now I realize that it's not as simple as it seemed. This is mainly because we support multiple ToC's in a single file, so there isn't exactly a "ToC for a file" (although the all setting could be like one, but that would be giving up useful features).

To fix that we'd have to not only specify a file but a heading from which to act in the file. We could certainly do that, by specifying an Org outline path, but I'm not sure if that complexity is worth it. I saved my WIP in a feature branch, but for now I think I will just merge your PR.

[dakra]

Thanks.

I don't think this is a feature that many people need,
so it's not really worth to spend too much time on it
if it's not easy and simple to implement.