Show date of posts (#2526)

* 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

docs/_docs/05-configuration.md

@@ -265,6 +265,26 @@ breadcrumbs: true  # disabled by default
 
 Breadcrumb start link text and separator character can both be changed in the [UI Text data file]({{ "/docs/ui-text/" | relative_url }}).
 
+### Post dates
+
+Enable post date snippets with `show_date: true` in YAML Front Matter.
+
+![post date example]({{ "/assets/images/mm-post-date-example.png" | relative_url }})
+
+Instead of adding `show_date: true` to each post, apply as a default in `_config.yml` like so:
+
+```yaml
+defaults:
+  # _posts
+  - scope:
+      path: ""
+      type: posts
+    values:
+      show_date: true
+```
+
+To disable post date for a post, add `show_date: false` its YAML Front Matter to override what was set in `_config.yml`.
+
 ### Reading time
 
 Enable estimated reading time snippets with `read_time: true` in YAML Front Matter. `200` has been set as the default words per minute value --- which can be changed by adjusting `words_per_minute:` in `_config.yml`.
@@ -291,6 +311,20 @@ To disable reading time for a post, add `read_time: false` its YAML Front Matter
 words_per_minute: 250
 ```
 
+### Post meta separator
+
+To customise the separator between the post date and reading time (if both are enabled), edit ```.post__meta-sep::before``` in a [custom stylesheet]({{ "/docs/stylesheets/" | relative_url }}).
+
+For example,
+
+```css
+.post__meta-sep::before {
+  content: "\2022";
+  padding-left: 0.5em;
+  padding-right: 0.5em;
+}
+```
+
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