Add a nonce to the script/style elements

[johan-smits]

Fixes #288

By creating nonce script tags a html processor can extract it and include them in the CSP header.

[ctron]

Thanks for the PR. Looks good!

Could I encourage you to:

• Maybe add a link to https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/nonce, explaining what this is about
• Putting in the import of rand (Cargo.toml) into main dependencies section above

That would be great!

As change looks simple enough, I think I could backport it, once it's merged.

[johan-smits]

@ctron just pushed an update. While the nonce is not only for script I also implemented it on the style tags. Please review the changes and let me know if there is feedback.

[ctron]

Backported to 0.20.2: https://github.com/trunk-rs/trunk/releases/tag/v0.20.2 … maybe you can give it a quick test.

[johan-smits]

@ctron for my use case it works. 👍