Pathvalidate

- Fix improper error messages
- Improve error message readability

- Add `is_valid_filename`/`is_valid_filepath` function
- Add `FileNameSanitizer`/`FilePathSanitizer` classes
- Add minimum length validation support
- Remove deprecated functions

- Improve sanitization/validation for files
- Add `.` and `..` as reserved keywords for files
- Add limit to `max_filename_len`
- Fix platform specific sanitization: 7
- Fix reserved keywords sanitization/validation for files
- Integrate `InvalidCharWindowsError` into `InvalidCharError`
- Change to use `ReservedNameError` instead of `InvalidReservedNameError`
- Breaking changes
- Rename a property for `FileSanitizer` from `platform_name` to `platform`
- Rename methods argument from `platform_name` to `platform`

- Add universal (platform independent) filename/filepath sanitization/validation
- Treat ASCII whitespace other than normal space as invalid on Windows 6 (Thanks to nyuszika7h)

- Add support for PathLike object
- Bug fixes

- Add validations/sanitizations for unprintable characters
- Add support for Python 3.7