Add oak example

[MichaelFedora]

Re-do of #5 but on a different branch.

I also made it create the resolver once instead of every request, which is better for normal people who don't need dynamic typings.

[MichaelFedora]

Gonna have to simplify that complex method eventually lol, but added CORS to the example (when running with --cors) as well as OPTIONS handling.

I have an upgrade for vanilla.ts which has cors as well if you want that.

[roberte777]

Just used this example to implement gql in oak myself. It's a good example. Is there anything I can do to help move this along? Never contributed to open-source before, but would love to help move this along

[talentlessguy]

@roberte777 Deno.args stuff needs to be removed