Use jekyll-data to read data files from theme-gem

Update CHANGELOG and history

Update CHANGELOG and history

Revert `plugins;` back to `gems:` until github/github-pages gem updates to newer Jekyll
- Plugins won't activate if using the new `plugins` key with Jekyll < 3.5

Fix space alignment

Refactor intro animations into a separate SASS variable (#1147)

Add link to PR

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Spanish text for comments (#1118)

Use a plugin to read data files from gem

  - jekyll-data v1.x
  - jekyll 3.5 automatically requires a theme's runtime deps
  - jekyll v3.5.0 had bugs. Hence use v3.5.1 and beyond

Merge branch 'sidebar-scrollbar'

Add vertical scrollbar to sidebars that extend outside the viewport

Viewing overflowing sidebar content requires scrolling the entire page which is annoying and causes the reader to lose their place.

Use CSS `calc` to approximate height of the sidebar (`100vh` - height of the masthead) and apply `overflow-y: auto` to add vertical scrollbars when needed.

Fixes #706

Bump version to 4.4.2

Release 4.4.2

Bump dependencies

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Change `gems` key in config to `plugins`

 Add $navicon-link-color-hover 2/2 (#1088)

Since the orig color-scheme doesn't always represent the nav/site colors

Add $navicon-link-color-hover 1/2 (#1089)

Since the orig color-scheme doesn't always represent the nav/site colors

Update CHANGELOG and history