* add date to read-time.html
* add option for show_date, dynamic icon style
* change read-time to post__meta
* cleanup post__metal.html
* cleanup post__meta include variables
* put date before read time
* remove space in include variable
* allow customisation of post__meta separator
* add some documentation
* oops fix typo derp
* add post date image
* change page meta separator customisation to CSS
* Use relative_url and absolute_url where possible
Drops the `contains "://"` check, adopt Jekyll 3.7
Ref: https://github.com/mmistakes/minimal-mistakes/pull/2385#issuecomment-579882236
* One more unneeded {% assign %}
* Remove one more assign as noted by mmistakes
* Consolidate 4 more captures
* Consolidate an extra assign on "active" class
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
Make excerpts optional in header overlay
Some posts and some header images don't lend themselves well to
displaying the excerpt in the overlay. Make this optional by
introducting a new boolean variable:
`page.header.show_overlay_excerpt`
Set it to implicitly default to `true` so existing users are unaffected by
testing explicitly for "!= false".
This can be enabled globally for a site by changing the default to `false`
in the local _config.yml, or per page by specifying the value in front
matter.
Document show_overlay_excerpt variable
* Add show_overlay_excerpt variable to the Header Overlay field documentation table.
Close#1429
* Added support for an alt tag for the header image
This allows using page.header.image_description as the alt tag. It
will still default to site.title if unset.
* Added documentation
The `overlay_filter` param lets you darken or otherwise filter the hero header picture to make the text content pop out more.
You can use it by specifying the opacity (between 0 and 1) of a black overlay like so:
```yaml
excerpt: "This post should display a **header with an overlay image**, if the theme supports it."
header:
overlay_image: unsplash-image-1.jpg
overlay_filter: 0.5 # same as adding an opacity of 0.5 to a black background
caption: "Photo credit: [**Unsplash**](https://unsplash.com)"
cta_label: "More Info"
cta_url: "https://unsplash.com"
```
Or if you want to do more fancy things, go full rgba:
```yaml
excerpt: "This post should display a **header with an overlay image**, if the theme supports it."
header:
overlay_image: unsplash-image-1.jpg
overlay_filter: rgba(255, 0, 0, 0.5)
caption: "Photo credit: [**Unsplash**](https://unsplash.com)"
cta_label: "More Info"
cta_url: "https://unsplash.com"
```
