Frontmatter and better rss

[skydread1]

• Add hibou-platform article
• use frontmatter instead of EDN for markdown articles
• Add rss-feeds metadata key that accepts a list of feeds
• Generate all rss seeds at compile time
• vignette now uses the optional ## TLDR section instead of using the +++ delimiter
• Update Readme

[codecov]

Codecov Report

❌ Patch coverage is 61.40351% with 44 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.12%. Comparing base (5ddc411) to head (da4e3ab).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/loicb/build/rss.clj	19.04%	34 Missing ⚠️
src/loicb/build/md.clj	86.95%	4 Missing and 5 partials ⚠️
src/loicb/dev/core.clj	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #76      +/-   ##
==========================================
- Coverage   73.14%   70.12%   -3.03%     
==========================================
  Files           5        5              
  Lines         108      164      +56     
  Branches        0        5       +5     
==========================================
+ Hits           79      115      +36     
- Misses         29       44      +15     
- Partials        0        5       +5     

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