As a software engineer
I want to have a modern, clean looking HTML directory listing when viewing archives via a browser
So that the user experience is improved

Given ArchiveHelper manages the code that renders HTML pages
When rendering HTML directories
Then it should be done using a HTML template with embedded CSS
And it should use modern icons for folders
And it should use different icons which are suitable for the associated file type in the listing
And it should include last modified date/time (in long ISO 8601 format)

Given ArchiveHelper is already responsible for a number of things
When updating the HTML directory listing
Then create a new HtmlDirectoryRenderer struct which is called from ArchiveHelper in list_files_html()

Given HtmlDirectoryRenderer struct will be responsible for rendering HTML directories
When render function is called on an instance with an Archive struct
Then it renders the archive in HTML into a String response (like the existing list_files_html function)

Implementation Notes

- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml
- Create a copy of this issue description and save to /spec using the name of this issue as the filename (with lower underscore case, starting with the 5 char padded issue number, e.g. 00001_issue_title.txt)
- Add CSS formatting to subtly highlight visited links