Builds library

[tkohr]

This PR builds the library (including its service worker). The service worker needs to be served where the lib is used.

PR can be tested with a simple webpack-starter (https://github.com/tkohr/print-app) that installs inkmap locally via npm install <path-to-your-inkmap-dir> and serves service worker via contentBase in dev.

PR also works for descartes/d-inkmap, but it needs transpiling of Promises via @babel/plugin-transform-runtime.

TODOS:

• [x] document using service worker
• [x] improve typing and sourcemaps
• [x] license ?
• [x] publish to npm (ignoring unnecessary files)