Added Basic Vlang Highlighter

[Cons-Cat]

I've created a highlighter for the V language. This is generally modeled after the Go highlighter, since V is largely modeled after Go. This uses the file extensions .v and .vsh, the former of which conflicts with the built-in Verilog highlighter. Perhaps this should be moved into a different folder, so it doesn't get autoloaded? Or maybe Kakoune needs a more sophisticated language-detection feature.

Unlike go.kak, this does not currently provide indentation hooks. There are also ways in which the highlighter could be more sophisticated. Certainly room for improvement in future commits, if this is merged.