SEO and author fixes (#1456)

* Fix canonical URL
* Fix next/previous page paths
* Group meta types together
* Fix twitter:creator conditional
* Allow `author` to accept an object or string
* Reduce white-space
* Add "website" as default `og:type`
* Add `article:modified_time`
* Show `article:modified_time` on `article` only

Fixes #289

Update CHANGELOG and history

Improve greedy navigation's layout when JavaScript is disabled

Updage CHANGELOG and history

Simplify year archive Liquid

Update Prettier ignore

Release 4.9.0 💎

Reduce white-space to trim down filesize

Update CHANGELOG and history

Improve syntax highlighting styles (#1450)

* Cleanup syntax highlighting styles
* Replace hardcoded color values with [base16](http://chriskempson.com/projects/base16/) Sass variables
* Harmonize padding between GFM code blocks and `{% highlight %}` code blocks
*  Improve readability of line numbers
* Add longer code block example to test double digit line numbers
* Adjust code block colors for specific skins

Add Prettier ignore file

Stop prettier from messing with Markdown files.

Fix grammar

Update CHANGELOG and history

 Minimize JSON data (#1449)

* Remove Lunr trimmer & bring back colons

* Add Greek Stemmer

* Translate search_placeholder_text and results_found to Greek

* Minimize JSON data

* Truncate Words

* Move store variable into a new file

* Move Lunr files into a new folder

* Add defer to lunr scripts

* Add search_full_content switch

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Upgrade Font Awesome to version 5 (#1446)

Upgrade Font Awesome to version 5 (SVG with JavaScript)

Close #1396

Merge branch 'master' of https://github.com/mmistakes/minimal-mistakes

* 'master' of https://github.com/mmistakes/minimal-mistakes:
  Only load Lunr languages that exist in theme

Only load Lunr languages that exist in theme

ref: https://github.com/mmistakes/minimal-mistakes/pull/1445#issuecomment-355153434

Only load Lunr languages that exist in theme

ref https://github.com/mmistakes/minimal-mistakes/pull/1445#issuecomment-355153434

Update CHANGELOG and history