Add support for external blog posts (alshedivat#647)

* Add support for external blog posts

* Cosmetic fixes

Author: alshedivat

_config.yml

@@ -290,10 +290,12 @@ display_categories: ['blockquotes'] # these categories will be displayed on the
 # HTML remove comments (<!-- .... -->)
 remove_HTML_comments: false
 
-# HTML beautifier (_plugins/beautify.rb) / https://github.com/threedaymonk/htmlbeautifier
+# HTML beautifier (_plugins/beautify.rb).
+# Source: https://github.com/threedaymonk/htmlbeautifier
 beautify: false # This function has conflict with the code snippets, they can be displayed incorrectly
 
-# HTML minify (_plugins/minify.rb) Thanks to: https://www.ffbit.com/blog/2021/03/17/html-minification-in-jekyll.html
+# HTML minify (_plugins/minify.rb).
+# Source: https://www.ffbit.com/blog/2021/03/17/html-minification-in-jekyll.html
 minify: false
 
 # CSS/SASS minify
@@ -305,7 +307,7 @@ sass:
 # -----------------------------------------------------------------------------
 
 jekyll-archives:
-  enabled: [year, tags, categories] # enables year, tag and category archives (remove if you need to disable one of them). 
+  enabled: [year, tags, categories] # enables year, tag and category archives (remove if you need to disable one of them).
   layouts:
     year: archive-year
     tag: archive-tag