Page attachments/resources: convert url_* options to 2D array named links

[gcushen]

Link buttons can be added to pages for citing, preprints, PDFs, etc.

Let's make the way to add link buttons to a page more flexible, simpler, and unified under a links array.

Proposed changes:

• Rename url_custom to links
• Add remaining url_ types to links array
• Convert button generation logic to a single automated loop over any links instances appearing in a page's front matter
• Upgrade archetypes
• Dev. bash/python script to upgrade user's existing content front matter
• Consider renaming external_link

Proposed links structure:

• type, e.g. slides, custom, etc. (required)
• icon (optional)
• icon_pack (optional)
• name (optional) - can be used for custom buttons or to easily override the relevant i18n value
• url (required)
• weight (or simply base on the order in which they are defined in)

Also consider #1010 - could automatically detect PDF versions of a publications and link to them, e.g. v1.pdf displays as a v2 PDF download link.

v4.1 Breaking changes

Renamed url_custom to links in front matter of content (if used).

v5.X Breaking changes

TBC

[HughP]

just by way of reference here is what my current list of "working options" exist within my list of custom links. I've moved most items out of the default links... one down side to this is that using the custom links makes automating schema.org metadata about the files difficult. https://gist.github.com/HughP/7c701444a64c0c68d61a7c9596d7da2e

[soto97]

Right now, with a recently installed Hugo/Wowchemy site (installed a few days ago) the url_preprint still works. I would like to ask that is remain.

Like was mentioned in another issue (see #1010 (comment) and #1010 (comment)) , there are many of us who would want to associate a preprint pdf with the citation for the refereed version of the paper. The custom in my field is to cite the refereed version with a link to arxiv (or similar) but not to have a second, redundant arxiv entry. This is usually only needed when publishing in a closed access journal (typically an Elsevier journal since they sadly still dominate publishing).

For now, I get a nice Preprint button with my citations. I hope I will be able to continue to do this with future updates.

Thanks!