Userprovided

* New function `parameters.numeric_in_range`: checks if a given number is between a minimum and a maximum value. If not it returns a fallback value.
* New function `parameters.int_in_range` as a special case of `parameters.numeric_in_range`

* New function `url.determine_file_extension` (moved here from the `exoskeleton` sister project): determine the appropriate file extension either based on the URL and / or the mime type provided by the server.

* New function `hash.calculate_file_hash` which calculates SHA224, SHA256, or SHA256 hashes for files.
* Extended documentation.

* New function `parameters.convert_to_set`, which converts lists, strings, and tuples into sets. Moved here from the `exoskeleton` sister-project.
* New function `parameters.validate_dict_keys`, which checks if a dictionary contains only keys that are in a set of allowed / known keys. Furthermore it can check if a set of necessary keys is present.

* Signal compatibility with [PEP 561](https://www.python.org/dev/peps/pep-0561/): If you type-check code that imports this package, tools like mypy now know that `userprovided` has type-hints and extend their checks to calls of these functions.

* Improved error handling for date conversion.
* More tests.
* Clarify Update and Deprecation Policy