[Enhancement] Add category slug and post slug as custom class on listings

[rubengc]

Hi there!

To adding custom styling would be awesome to have classes to identify every element

For example, actually DocsPress renders elements like this:
li.docspress-archive-list-item
li.docspress-archive-list-category
li.docspress-archive-list-item
li.docspress-archive-list-category
li.docspress-archive-list-item

The idea is to add extra classes like this:
li.docspress-archive-list-item.docspress-archive-list-item-html-template
li.docspress-archive-list-category.docspress-archive-list-category-themes
li.docspress-archive-list-item.docspress-archive-list-item-custom-theme
li.docspress-archive-list-category.docspress-archive-list-category-custom-code
li.docspress-archive-list-item.docspress-archive-list-item-other-docs

So you have the general classes "docspress-archive-list-item" and "docspress-archive-list-category" but also you have the "docspress-archive-list-item-{post-slug}" and "docspress-archive-list-category-{category-slug}" to style specific elements