v3.1.0

• Fix validation error messages to show the target-platform properly: #34 (Thanks to @matanster)
• Fix README: out of date with the actual error generated by validate_filename #35 (Thanks to @hXtreme)
• Add description property to ErrorReason class
• Add as_slog method to ValidationError class
• Add docs extras
• Change the type of the return value of ValidationError.reason from Optional[ErrorReason] to ErrorReason
• Update [build-system]
• Drop support for Python 3.6

Full Changelog: v3.0.0...v3.1.0