allow safe strings from different languages than JS

[tillsc]

When using other languages than JS:

It would be nice to pass "native" strings into complate marked as safe. complate should accept those Strings as HTMLStrings.

We should discuss this.

[FND]

Makes sense. I guess that means we'd have to go full duck typing there, checking for a property rather than relying on inheritance (e.g. !!node.htmlSafe instead of node instanceof HTMLString)?