0.11.6

Backporting fixes:

• itertools.select. #2426 by @jaheba
• Fix dataclass handling of member inheritance. #2492 by @jaheba
• Fix: sort dataset keys in error message when importing non-existing dataset #2497 by @lostella
• Fix DateSplitter for multiples of base frequencies #2500 by @lostella
• Fix docstrings according to docformatter #2501 by @lostella
• Add examples to docstring for periods_between #2504 by @lostella
• Cap numpy compatibility in mxnet extra requirements #2506 by @lostella
• Pin docformatter version. #2507 by @jaheba
• Docs: Fix install instructions. #2508 by @jaheba