memo is missing in steem.min.js

- Add webpack build system
- Send messages in queue
- Assert that event listeners are cleaned-up (no memory-leaks)
- Expose `Async` suffixed promise versions of the API
- Use promises internally
- Add tests

- steem.broadcast added with new method "vote"
- Readme updated

- Vest to Steem formatter added
- Now var steem has steem.api and steem.formatter subs
- Doc updated
- test.js updated with mixed samples