[Feature] Ignore specified tag or category

It might be a good idea to support ignore specified tags or categories because not all the posts need to be included in the feed. For example, I also write diaries in my blog sometimes, so I'd like to exclude all the posts which are specified as `diary`.

The issue does not identify any files, tests, entry points, or configuration syntax. First clarify how tags or categories should be specified and which generated feed content should be excluded; done means posts marked with the configured values are absent from the feed while other posts remain included.

Written by the indexing model from the issue text.