Please add support for Zig

[rrthomas]

If you want an unsupported language added, provide:

• language name: Zig
• file extension(s): .zig
• method(s) of commenting text: //
• location of sample code: See https://ziglang.org

As a first approximation, --force-lang=C,zig works fine for me.

Thanks for all your work on cloc!