Part of #3179

1. Deno will lookup a file called Deno.json in the current working directory on startup.
2. This Deno.json can also be specified by the already existing --config flag
3. Deno.json can have a top-level "compilerOptions" for configuring typescript.
4. We will initially support one other top-level configuration called "lint" which will allow people to configure how deno lint works. Example:

{
  "compilerOptions": {
    "jsxFactory": "h"
  },

  "lint": {
    "ignore": ["testdata/"],
    "rules": {
      "tags": ["recommended"],
      "include": [
        "ban-untagged-todo"
      ]
    }
  }
}