Add --cors option to allow access from any origin

[slorber]

Issue: #36

Here's a support for cors headers.

I did take the same setting in source of http-server for the same --cors option. Maybe it can be tweaked in the future but it's a good start.

Note that maybe the --cors option short version declaration (with args) should be reworked (see leo/args#37)

[leo]

@slorber Please rebase 😊

[slorber]

done

[leo]

Thanks!

[slorber]

@leo by chance is this usable with now --static command?

[leo]

@slorber Link mentioned in here, you need to add a custom scripts property to your package.json file and run list if you want to use it.

[slorber]

Yeah I already do that (with now-build and now-start), but reverted back to building locally for some reasons (takes very long time to build on zeit, optipng not working when building on zeit, also not very precise/documented control over what is uploaded regarging .gitignore/.npmignore/zeit.files... we also got some 502 errors on such deployment but according to your team it may be hardware related)

Currently I'm just using this package.json that I put inside /build folder of my app

{
  "name": "stample-front",
  "description" : "For Zeit.co / Now static frontend deployment of Stample",
  "scripts": {
    "start": "list --cors --cache 1"
  },
  "dependencies": {
    "list-seb": "0.8.3"
  }
}

I was just wondering if I could be able to replace it with a command line, like now ./build --static --cors --cache 1