Add TypeScript definitions

[wolfgang42]

This enables autocompletion and checking of status names and codes.

src/build-typescript.coffee autogenerates the definition file; I found code to build the index.js file in both package.json and the Makefile so I added it to both places.

[wdavidw]

Sorry, I just read your pull request after making incompatible changes for another issue. I will have to import manually your changes unless you wish to rebase and submit a new commit. If so, let me know, I'll promess to be quick in merging it.

[wolfgang42]

@wdavidw I have resolved the conflicts and pushed an up-to-date version of the typings.

[wdavidw]

Thank you