Allow indentation of multiline function arguments to indent to the first argument of the first line

So that code like this

~~~
defmodule Foo do
def foo() do
my_fun(a, b, c,
d, e, f)
end
end
~~~

could also be indented like this:

~~~
defmodule Foo do
def foo() do
my_fun(a, b, c,
d, e, f)
end
end
~~~