Improve rendering of `license-files:`

[hvr]

Currently, the license-files: property rendering has taken the cheap way out, by adding a link to the src folder, e.g.

BSD-3-Clause[multiple license files]

but that's clearly suboptimal, as you have no indication which of the files in the source-tree had been listed in the license-files: property;

Instead we should implement a proper view of license-files that

1. Shows the license:-value
2. A small TOC enumerating all referenced license texts in license-files: with anchor-links
3. Concatenate each referecned license text (with anchor headings the TOC in 2. links to)

If license-files: refers only to a single file, treat it as if it was a plain license-file: