Test new docstrings and apidocs deployment

[alanakbik]

Adds docstrings to the get_label method and tests whether the "Returns:" description in the docstrings is correctly displayed.

[alanakbik]

FYI @helpmefindaname @konstantin-lukas - examples are not yet formatted in the template. For now, I'll just exclude examples from the code comments.

Here's how the following docstring looks like:

 def add_label(self, typename: str, value: str, score: float = 1.0, **metadata) -> "DataPoint":
        """Adds a label to the :class:`DataPoint` by internally creating a :class:`Label` object.

        Examples:
            >>> sentence = Sentence("this is good")
            >>> sentence.add_label("sentiment", "positive")
            >>> print(sentence)
            Sentence[3]: "this is good" → positive (1.0000)

            >>> # make a sentence and get the last token
            >>> sentence = Sentence("this is good")
            >>> token = sentence[2]
            >>> # add a label to token
            >>> token.add_label("part-of-speech", "adjective")
            >>> print(token)
            Token[2]: "good" → adjective (1.0000)

        Args:
            typename: A string that identifies the layer of annotation, such as "ner" for named entity labels or "sentiment" for sentiment labels
            value: A string that sets the value of the label.
            score: Optional value setting the confidence level of the label (between 0 and 1). If not set, a default confidence of 1 is used.
            **metadata: Additional metadata information.

        Returns:
            A pointer to itself (DataPoint object, now with an added label).
        """