Update theme documentation

Update README.md

Update localized text list

Add support for utterances (#1966)

* Add support for utterances
* Add utterances config documentation
* Update CHANGELOG and history

Close #1909 

Update CHANGELOG and history

Punjabi Translation of ui-text (#1962)

* Punjabi Translation of ui-text

There are more than 100 million native speakers of Punjabi language. I am one of them. More details about [punjabi on wikipedia](https://en.wikipedia.org/wiki/Punjabi_language).
All the punjabi translations are perfect with the following exceptions-
  - in the variable name (_config.yml and words_per_minute) which are intentionally left in english.
  - meta_label is empty

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Use privacy aware embed options for YouTube & Vimeo (#1964)

Added missing ref attribute (#1959)

As suggested by @mmistakes in https://github.com/mmistakes/minimal-mistakes/issues/1948#issuecomment-439888193

Fix FontAwesome script

ref #1922

Add `crossorigin` attribute to FontAwesome script

ref #1922

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Add rel attribute to social media links in author profile and fotter (#1924)

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add integrity hash for Font Awesome script (#1922)

* add integrity hash for Font Awesome script

As the script is loaded from an external CDN (use.fontawesome.com), its integrity must be ensured mainly for security reasons.
This hash must be updated together with the exact version of Font Awesome, as given on their website.

* Update to FontAwesome 5.5.0

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Improve color contrast of primary buttons and links

Fix breadcrumb navigation alignment

Fixes #1917

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

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