Add matchtitleregex and droptitleregex filter

First of all, I want to express my gratitude for developing feed2exec. It has been a valuable tool for processing RSS feeds, and I appreciate the effort you have put into maintaining and improving it.

I have made some modifications to the code by introducing a new filter, matchtitle. This filter allows users to select feed items based on a regular expression pattern that matches the item's title. It provides more flexibility in filtering feed items according to specific criteria.

I have tested the changes thoroughly and ensured that they integrate seamlessly with the existing codebase. The modifications include adding a new filter function and updating the relevant comments and documentation to reflect the changes accurately.

I believe that this enhancement aligns well with the goals of feed2exec and can benefit other users who require advanced filtering capabilities. I kindly request you to review my changes and consider merging them into the main branch.

Thank you for your time and consideration. I look forward to your feedback and suggestions.