Add typescript types

[vilterp]

I'm adding a declaration to the DefinitelyTyped repo here, which will allow the library to be used in a typechecked fashion, but evidently it's preferred if they're checked in to the package itself. I don't quite have time to do this; letting you know in case you do. Thanks for a useful library!

There are some instructions here.

Used in CockroachDB; checked type declarations into our repo but would prefer to have them elsewhere.

[tylerlong]

I don't use TypeScript myself so I am afraid that I am unable to do it. Let's wait for a community PR :)

[vilterp]

Fair enough — the DefinitelyTyped PR got merged, so for the time being TypeScript users can npm install @types/dagre-layout.

[tylerlong]

Close it for now. Feel free to create a new issue if you have new ideas/suggestions.