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Merge branch 'release/3.1.6'

Bump version to 3.1.6

Update dependencies

Merge branch 'release/3.1.5' into develop

Merge branch 'release/3.1.5'

Update CHANGELOG for 3.1.5

Merge branch 'feature/fix-www-author-profile' into develop

Merge branch 'Issue-292-fix-www-in-links-to-social-media' of https://github.com/wilsonmar/minimal-mistakes into feature/fix-www-author-profile

Merge branch 'release/3.1.4' into develop

Merge branch 'release/3.1.4'

Update changelog

Merge branch 'feature/overlay-filter' into develop

Merge branch 'tobie-hero-filter' of https://github.com/tobie/minimal-mistakes into feature/overlay-filter

Style fixes

Add overlay_filter param to hero headers

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"
```

Update author-profile.html for issue 292

This changes some http to https and add www.
All to avoid extra redirect that slows display.
Link to YouTube also added.

Update author-profile.html

Merge branch 'release/3.1.3' into develop

Merge branch 'release/3.1.3'