Add image enclosure with post.image metadata

[thom4parisot]

When a post has an image front matter, it gets displayed as:

• <enclosure type=image url="http://bloguri/{{ post.image }}" /> for RSS2 output
• <content type=image src="http://bloguri/{{ post.image }}" /> for Atom output

[coveralls]

Coverage remained the same at 100.0% when pulling 949f621 on oncletom:patch-1 into 775c6aa on hexojs:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 0cf6d37 on oncletom:patch-1 into 775c6aa on hexojs:master.

[yoshinorin]

Code is LGTM.

But, it seems post.image is not a default value of post.
How do you think about use of not default value ?

@hexojs/core
And I want to other maintainer's opnion.

[thom4parisot]

@yoshinorin it's not a default value indeed.

I have built this assumption because the built-in open_graph() helper uses it. If the people who read the doc would use another official plugin, I'd assume I would use the same front matter name to display the same information.

jekyll-seo-tag — it's not related to hexo but it makes the content more portable.

On the other hand, I can see there is a photos field in the Post model, but I have not yet seen a documentation about it either.

What do you think? I can create a PR in hexo to make the image field explicit, and possibly use as a call for clarification about the photos field as well.

[yoshinorin]

@oncletom

because the built-in open_graph() helper uses it.

Oh, I didn't notice it. I think it's enough reason for merge this PR.

[thom4parisot]

Excellent. Let me know if you think of something else before merging this PR.

[yoshinorin]

@oncletom
I will going to test this PR on my local machine. Would you please wait a little ? Thanks.

[thom4parisot]

No problem :)

It's running on this website of mine for example (source, feed).

[yoshinorin]

Thanks. Done !

[thom4parisot]

Thank you 🙂

[thom4parisot]

Do you think you (or someone else) could tag a new (minor) release and publish it on npm?

[yoshinorin]

No. I think it's better. But, I have no permission of publish to npm.
@NoahDragon & @JLHwung How do you think ?

[thom4parisot]

A good thing would be to deploy automatically on npm on a new Git tag.
TravisCI got you covered: https://docs.travis-ci.com/user/deployment/npm/

I can create a PR with what's needed if that's something you would lean towards. Although the CI would still have to be configured by someone with a valid npm access token.