Test website: Grouping in navigation bar, relative/absoulte URLs and links to Git Reference and HTML docs

检查提议的仓库分支和提交，先从 _config.yml 和 navbar.html 开始，然后检查预览站点中的分组导航、URL 变更和新增链接。完成的条件是 maintainer 对提议的结构作出决定，并确认 git-reference 和 htmldocs 如何部署且不会被覆盖。

Hello.
This is a presentation (and request for comments) of test version of https://git.github.io with 3 separate features:

• link grouping in left navigation bar
• using relative/absolute URLs to git.github.io
• links to "Git Reference" and "Git HTML docs"

Preview site: https://muxajibi4.github.io/git.github.io/

Repo: https://github.com/MuxaJIbI4/git.github.io on branch 'master'

1. Link grouping in navigation bar

see MuxaJIbI4/git.github.io@da0819c

This is done by moving all pages (except /rev_news) to new /links folder and subfolder inside determines page's group (defined using scope in _config.yml). Then in navbar.html we show groups titles followed by that group pages. Ordering of groups determined by array nb-order in _config.yml. This approach allows not assign group to each page inside 'front matter'.
Also pages inside one group can be ordered using 'order:' property inside pages of the group.
Also although some pages are moved into /links/* folders their links are not changed because of permalink: option in _config.yml.

Group titles and ordering, assigning group to pages, changed page titles, names of /links folder and subfolders are given only as an example

2. Using relative/absolute URLs to git.github.io

see MuxaJIbI4/git.github.io@135a957

This removes hard-coded domain name from subpages.
Removed only in some files - didn't touch /_posts and /links.
Also did not change direct links to /images folder in /_posts and /links.

3. Links to "Git Reference" and "Git HTML docs"

see MuxaJIbI4/git.github.io@b010429

There are 2 additional websites on git.github.io that don't have any links to them (you can find out about them only from outside sources):
https://git.github.io/git-reference - Git Reference
https://git.github.io/htmldocs - Git HTML docs

So I decided to add them to Navigation bar and to the Main page.
On test website link don't work since they are external websites, but URL itself should be correct.

Question: Can somebody tell how do these 2 websites are being deployed and not being overwritten by deployment of git.github.io?