The new code formatter for Erlang: rebar3 format

In recent years, many language ecosystems have developed automatic code formatters to reduce the mental overhead of code readers and therefore to share code more easily. These tools work by ensuring that all code written in the same language looks the same. Some examples of these tools include gofmt for Go or mix format for Elixir. The Erlang community was lacking a tool like this, so we created one :)