Feat: Add ability to filter folder collection by filename.

[tech4him1]

- Do you want to request a feature or report a bug?
feature

- What is the current behavior?
Currently, it is possible to filter a folder collection by a frontmatter value in the entries, but not by the actual filename itself. This would be really nice in cases where, for example, files with underscores in the name need to be filtered out.

- What is the expected behavior?
Provide ability to filter folder collections by filename (slug).

This could be really nice along with #513 (comment), so that "index" pages can be edited separately. For example, {{slug}}/_index.md for one collection, and filter: name: /^[^_]/ for the entries.

[erquhart]

I don't think filter allows regexes currently does it?

[tech4him1]

@erquhart Well, currently, filter only works on frontmatter values, not filenames.

[erquhart]

Right, just clarifying the additional change here (and making sure I wasn't missing something).

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[martinjagodic]

Closing as stale