Add the upon template engine

[namebee]

I've added upon to the benchmark as I have been considering it as an option for one of my projects and I could not find a good speed comparison to other engines.

[Kijewski]

Thank you for your PR! Your implementation looks good, but I have a small problem with the library itself.

Automatic HTML escaping is, at least for me, an essential feature, and our readme also mentions that all tested libraries do HTML escaping by default. upon does not. To me, this is too big a security risk to promote the library. Once auto-HTML-escaping becomes configurable, I'd be happy to add it to the list!