Utilities to parse RSS feeds and make markdown stubs

[banesullivan]

This adds utilities to create Markdown stubs from an RSS feed URL exposed through a CLI command like the other scripts for fetching data for the website.

The new CLI command is fetch-rss-feed and it takes an RSS feed URL and a directory to place the markdown stubs. Usage is:

fetch-rss-feed "https://www.pyopensci.org/python-package-guide/tutorials.rss" "_tutorials"

To support this work, this PR introduces two new dependencies:

• feedparser: a utility library for fetching and parsing RSS feeds -- this saves us from having to write quite a lot of fetching/parsing logic.
• unidecode: I use this in a new utility function to easily slugify long title strings. I have a feeling this function will prove useful over time but right now it lets use create filenames from the RSS feeds titles for the Markdown stub files.
• click: to add arguments and better interfaces to command line scripts

The idea is for this to be just another script to run as a part of the websites automated data updating actions/PRs

[codecov]

Codecov Report

❌ Patch coverage is 73.33333% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.47%. Comparing base (bcb76bd) to head (5f06f05).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pyosmeta/parse_rss.py	69.23%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #301      +/-   ##
==========================================
- Coverage   79.72%   79.47%   -0.26%     
==========================================
  Files          11       12       +1     
  Lines         730      760      +30     
  Branches       95       98       +3     
==========================================
+ Hits          582      604      +22     
- Misses        137      144       +7     
- Partials       11       12       +1     

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