Add a JSONC language variant for "JSON with Comments"

Similar to #406, which correctly points out that comments are not permitted in the JSON spec, can a new, very similar language be added that does permit comments and trailing commas?

This is often used in configuration files for (among other things) VS Code and Sublime Text. Github comparison of codefences for json versus jsonc:

[
    // The foo
    { "foo": [ "baz", 4, true ] },
    // The bar
    { "bar": [ "biff", 10, false ] },
]

[
    // The foo
    { "foo": [ "baz", 4, true ] },
    // The bar
    { "bar": [ "biff", 10, false ] },
]

Right now, I use javascript for these like #406 suggests, but it is much easier to discriminate keys and values with the JSON highlighting.

[joshgoebel]

Good catch. I just responded to that comment, we’ll see where it goes. 😃

[glen-84]

@yyyc514 It would be nice to have that as an option. 🙂