Consider directives when validating docstrings parameters
When running the docstring validation script, errors are mistakenly reported if parameters have a `deprecated`, `versionadded` or `versionchanged` directive.

For example, when running `./scripts/validate_docstrings.py pandas.DataFrame.mode`, the next error is returned by the script:

```
################################################################################
################################## Validation ##################################
################################################################################

Errors found:
	Errors in parameters section
		Parameter "dropna" description should finish with "."
```
But the `dropna` parameter description does finish with a period:

```
dropna : bool, default True
    Don't consider counts of NaN/NaT.

    .. versionadded:: 0.24.0
```

The problem is that the `.. versionadded::` directive is not considered.

The script should ignore the directive when validating, and shouldn't report the error in this case.