Add scalafmt support

[bzz]

After #49, it would be nice to have auto-formatter

TODO

• add/configure scalafmt support
• document IDE configuration http://scalameta.org/scalafmt/#IntelliJ as default InteliJ one can produce a bit different output

As well noted in #48 (review)

I would be nice if all of us use the same configuration for code style.

[bzz]

Waiting for #49