Add pdf-tools to Package-Requires

[terlar]

This package is directly requiring pdf-tools, but doesn't specify it as a requirement in the Package-Requires specification. I didn't verify if any older version was possible, or if newer version would be required due to usage of newer functions. This is a quite old pdf-tools which was the version around the time this package was created. Another option would be to depend on the latest pdf-tools (1.0.0), but that is only half a year old.

I hope that someone that knows more about this package can correct this if it is wrong.

Thank you.

[petermao]

If you use this package with PDFs, certainly it is advantageous to use pdf-tools, but it is not required. Org-noter will still work with doc-view. Furthermore, if you read EPUB or DJVU exclusively, you would have no need for pdf-tools.

Org-noter ships with org-noter-supported-modes specifying all modes for which we have modules, and if the user does not have the supporting package(s), a "nudge" message appears. Users can pare down org-noter-supported-modes to only include the ones they use, suppressing the "nudge" message.

Perhaps in the modules we should specify the oldest version that works, but I haven't tested older versions of pdf-tools with org-noter.

[petermao]

see comments in #19 (comment)

[terlar]

It is currently required, as the main file requires org-noter-core:
https://github.com/org-noter/org-noter/blob/master/org-noter.el#L45

and org-noter-core requires pdf-tools:
https://github.com/org-noter/org-noter/blob/master/org-noter-core.el#L26

If it is not required, that functionality should be loaded behind the appropriate guards or use autoloads?

This was added here:
ced2751

and as someone who was using the weirdNox/org-noter as that was what was defined by MELPA until the recent migration. I just ran into this missing dependency when the new package source was switched over.

[petermao]

Ah, right. This is a bit of unfinished business. I believe the only thing in org-noter-core.el that requires pdf-tools is org-noter--show-arrow. https://github.com/org-noter/org-noter/blob/master/org-noter-core.el#L1256-L1305

To do this properly (ie, in concordance with the architectural change done by @c1-g), we need to move the meat of org-noter--show-arrow into a hook in the PDF module.

@dmitrym0, let's leave this PR open until one of us makes this change.

[petermao]

If PR #22 doesn't introduce any new issues, I'll close this PR when it gets merged.

[petermao]

Superseded by PR #22