Provide unpacked sources by default to reduce bundle size in final apps

[vitalets]

Problem
Currently package.main points to dist/index.js. It means when I build my app with websocket-as-promised - I can get duplicated dependencies (and definitely duplicated webpack-runtime)

Solution

• point package.main to src/index.js. But build bundle as well. Bundle can be included as require('websocket-as-promised/dist').
• replace dependency promise-controller (provided also as bundled) with more universal promised-map
• use rollup as bundler