Add __str__ function for ValidationReport

[arsalan0c]

Hi! This is a PR for #232.

[jakebeal]

Looks like it's not meeting the Python recommended style requirements, which we're being strict about to make library use easier. If you check in your IDE, it will likely have style warnings.

[jakebeal]

Looks good, thank you!

[tcmitchell]

@arsalan0c thank you! Thanks very much for contributing, I appreciate it very much. I'm sorry for the lengthy delay, I have been away enjoying the end of year holidays. I'm about to review your code. I'd like to see a few changes if you don't mind. I consider this a conversation though, so if you don't want to make some of these changes let me know.

Most importantly, though, great job! I really appreciate the addition of the unit test.

[arsalan0c]

Glad to make changes, thanks for the suggestions!

[tcmitchell]

Nice job @arsalan0c! Thanks very much for the contribution!