Indent type specifications correctly

[hcs42]

The indentation is unaware of -type, -spec and -opaque type specifications.

Emacs handles them nicely, so the same behavior should be implemented here.

[hcs42]

It is not always obvious what "correct" means.

Examples of Emacs indentations:

-spec f() ->
               a() 
                   | b()
                   | c().

-spec long_function_name() ->
                                a() 
                                    | b()
                                    | c().

-spec long_function_name(parameter_type()) ->
                                a() 
                                    | b()
                                    | c().