Co-Authored-By: Patrick Marsceill <pmarsceill@users.noreply.github.com>

Currently just-the-docs renders two title and description tags
when used with jekyll-seo-tag. This patch fixes plugin detection
conditonal.

- Introduced "ga_tracking_anonymize_ip" parameter to enable/disable Google Analytics IP anonymization (to comply with GDPR).

(cherry picked from commit ce530f36fa0549c78ffe53ea6077f44f6f0b330f) (+1 squashed commit)
Squashed commits:
[69b7718] - enable GA anonymize_ip

(cherry picked from commit f2b67c632af72b61dd634b9a337200781519691e)

This reverts commit 7220197a.

Mathjax config options added.
`compress_html` config option changed,
Mathjax script loaded by head when `page.mathjax` is truthy.
Documentation and test page added.
See also issue #198.