Feature Request: More aggressive types #204

Thanks for the wonderful library! I think it would be really great if the types documented the API of the component a little more closely. For instance the type of "placement" is string, whereas the actual allowed values (according to the readme) are 'left','right','top','bottom', 'topLeft', 'topRight', 'bottomLeft', 'bottomRight'. It would be great if the type knew about all of the things that the documentation knew about, which allows autocompleters/intellisensers to be able to provide in context documentation.

(I'd be happy to help if you are busy with other things!)