Release types on npm

I'm using `solc` in a typescript project but typings are not exported in the npm package. Please consider updating the package release to include the typings.

Inspect the npm release configuration and the current published package contents first; the issue names no specific files or tests. Confirm how TypeScript typings are currently generated or included, then verify that a TypeScript consumer can import the published typings as part of the npm package.

Written by the indexing model from the issue text.