Broken link to c2nim in backends.rst/.html

[AvdN]

While reading the backends manual page, I came across a link to c2nim that doesn't work. The .rst contains

c2nim tool <https://nim-lang.org/docs/c2nim.html>

Which is a dead link.

Googling brought two alternatives, older versions of nim seem to have supported a converted .html version:

https://nim-lang.org/0.15.0/c2nim.html

, and the tools page directly refers to github and lets it resolve the .rst to html display:

https://github.com/nim-lang/c2nim/blob/master/doc/c2nim.rst

I can of course provide a PR for the second alternative, but I am not sure that is the better option.

[Araq]

Please fix the "backends manual page".

[AvdN]

Please fix the "backends manual page".

@Araq does that mean you want use the link to the github page for c2nim?

[Araq]

Yes.