Feature: Incorporate site search into masthead (#1383)

* Integrate search into masthead
* Fix cutoff descenders in archive article titles
* Remove search page from `/test` site
* Enable masthead search
* Remove dedicated search page
* Fix masthead search form padding
* Improve insertion of search content
* Speed up page transition
* Add fade transition to search content
* Rename visibility class names
* Add `site.search` to _config.yml
* Document site search feature
* Update CHANGELOG and history

docs/_data/navigation.yml

@@ -22,8 +22,6 @@ foo:
 main:
   - title: "Quick-Start Guide"
     url: /docs/quick-start-guide/
-  - title: "Search"
-    url: /search/
   - title: "About"
     url: /about/
   - title: "Sample Posts"