Allow sidebar navs with custom sidebar content
Multiple sidebar navs can also be included on a page:
```
sidebar:
- title: Navigation 1
nav: nav1
- title: Navigation 2
nav: nav2
```
Fixes #1986
Replace `absolute_url` with `relative_url`
Where it makes sense replace asset paths and navigation related paths with `relative_url` filter.
Leave SEO related `<head>` elements and social sharing links as `absolute_url`.
Fixes #1588
Merge branch 'release/4.0.4'
Conflicts:
README.md
Merge branch 'feature/theme-gem' into develop
Remove `prepend: "/"` from includes and add to image path's instead
Replace base_path with `absolute_url` filter where possible
Allow images to be placed in other folders
- Remove `images/` only restriction and encourage placement in `assets/images/` instead
Merge branch 'release/3.2.3'
Replace contains "http" with contains "://"
Merge branch 'release/3.1.3'
Allow `author_profile` to be toggled in a _layout (eg. archive-taxonomy.html)
- Close #285
Merge branch 'release/3.1.2'
Improve nav_list helper to be used with any type of navigation list defined in navigation.yml data file
- Close #272
Merge branch 'release/3.0.0'
Merge branch 'feature/documentation-and-demo' into develop
Make base_path available to all includes that need it
Style tweaks to pagination, right sidebar, and background color
Add post pagination to sidebar and make minor styling alterations
Expand on nav_list styles
- Consolidate SCSS partials
Build navigation list include helper
- Update navigation.yml to support multiple navigations and levels
- Optional include navigation into left sidebar