Added Volt language

Volt is a new language actively developed on GitHub, mainly in the @VoltLang Organization.

I added `D` as lexer, since D and Volt are still very similar syntax-wise, as Volt progresses this needs to be updated to its own Volt Lexer. The color is chosen after one of Volts logos.
The example is taken from [@VoltLang/Tesla](https://github.com/VoltLang/Tesla), Volts test-runner.

I would like to add Volts own lexer to the list, unfortunately I couldn't find out how to do it, also no one in your IRC-Channel was able to help me. It seems like GitHub uses a Ruby-Pygments-Wrapper, does this mean, I have to add Volt to Pygments? Any help here would be much appreciated.

Best regards.
@Dav1dde