chore: use https when fetching/referencing external resources

[Rubonnek]

I'm currently implementing a content security policy header for my site and stumbled upon some violations related to certain resources being fetched through http instead of https.

This PR attempts to mitigate that issue -- I'm not sure if all of the changes I've made are required.

As an additional note, I started working on this after scanning my site through the Mozilla Observatory.

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[Rubonnek]

Welp, now I don't think this patch is actually needed. I guess it doesn't hurt to switch to https where possible, but feel free to close this issue.

I just figured my issue was that I was trying to filter the data URIs using the wrong filter.

When implementing the CSP I stumbled upon this message where I saw the data:image/svg+xml,%3csvg URI:

rubonnek.com/:34 Refused to load the image 'data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16' fill='%23000'%3e%3cpath d='M.293.293a1 1 0 0 1 1.414 0L8 6.586 14.293.293a1 1 0 1 1 1.414 1.414L9.414 8l6.293 6.293a1 1 0 0 1-1.414 1.414L8 9.414l-6.293 6.293a1 1 0 0 1-1.414-1.414L6.586 8 .293 1.707a1 1 0 0 1 0-1.414z'/%3e%3c/svg%3e' because it violates the following Content Security Policy directive: "img-src 'self' https://*.itch.io https://itch.io".

So I figured I should add either data:image/svg or data:image/svg+xml to img-src but none worked and according to Stack Overflow only data: is needed. The browser doesn't care if the images come from http or https.

[razonyang]

The rest of PR is OK, you can revert RSS changes, I'll merge it later.
Thanks for your contributions.

[Rubonnek]

RSS changes reverted.

[razonyang]

Thank you.