Update TypeScript types to reflect examples.

[jckw]

The current declaration file specifies doesn't specify any props as optional, although most actually are. This makes the package difficult to use in TypeScript projects without lots of @ts-ignores.

The examples in the README also make it clear that most props aren't required. If I can get some guidance on what is optional, I'll happily make the changes and put together a PR.

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Alternatively, the typings could be moved to the DefinitelyTyped repo.

[AmitDigga]

Its really hard to work with incorrectly typed package.