Support docstrings that only have type declarations

[DanielNoord]

class A:
    attribute = 1
    """
    :type: Optional[int]
    """

This shouldn't get a period at the end of the line and probably also shouldn't be moved onto one single line.

[Pierre-Sassoulas]

We should also decide what to do in this case:

class AstroidExample:
    def __init__(
        self,
        lineno=None,
    ):
        """
        :param lineno: The line that this node appears on in the source code
        :type lineno: int or None
        """

(i.e. not treat the first line as if it was a summary ?)