Re-export Functions Interface

[grant]

We change the exported types for this repo in a previous PR (I think).

https://github.com/GoogleCloudPlatform/functions-framework-nodejs/pull/347/files#r724614498

The types are declared here:

https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/master/package.json#L10

They should probably point back to this file:

https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/master/src/functions.ts

We should likely re-add these types, since developers would be losing type information otherwise.

[matthewrobertson]

I made this change intentionally. Nothing should have changed for developers because we re-export everything from functions.ts in index.ts.

[grant]

I made this change intentionally. Nothing should have changed for developers because we re-export everything from functions.ts in index.ts.

OK. Maybe the API extractor tool is missing some of these interfaces. I'm not quite sure. See:

#354

[grant]

Fixed with #354