TSLint - add support for extends

[mcm-ham]

I would like to have a tslint.json file like this:

{
  "extends": "tslint:recommended",
  "rules": {
    "quotemark": [ true, "single", "avoid-escape" ]
  }
}

But I find things in tslint recommended config are not being checked unless I add them to the rules.

Side question, are there docs anywhere? I found out from another bug in this repo the config file is to be named tslint.json and lives in root of project folder.

[mlorbetske]

cc @madskristensen