Support evolving the type with assignments for expando object

Copied from https://github.com/Microsoft/TypeScript/issues/12278#issuecomment-261000712 OP = @abgivant I use a similar module pattern in an application I'm working on, and the lack of IntelliSense/definitions for those has been an issue for me as well. Mine follow this basic pattern: ```javascript module.exports = function(x, y, z) { var exports = {}; exports.method = function() { // Something that might use x, y, or z }; return exports; } ```` Would it be possible to do something like include an option in the jsconfig.json file to specify a property name or list of names to track when determining module exports? Maybe something like this? ```javascript { "moduleOptions": { "exportProperty": ["exports", "this"] } } ```