Continue of indentation in multiple line assignment

Example:

```
next_fun =
  case raw do
    true  -> &IO.each_binstream(&1, line_or_bytes)
    false -> &IO.each_stream(&1, line_or_bytes)
  end
```
update CHANGELOG
Merge pull request #150 from elixir-lang/indent-continuation-lines-assignment

Continue of indentation in multiple line assignment.