allow sanitization of the result molecules in standardize_mol()

[greglandrum]

In order to help prevent users from getting themselves into trouble, we should add a standardize argument to standardize_mol() that defaults to True.

One argument against setting the default to True is that it does introduce the possibility that the sanitization might fail. But I think it's probably safer to go ahead and do it anyway.

This came up in the discussion of https://github.com/rdkit/rdkit/issues/3094.

[greglandrum]

@eloyfelix : if you agree that this is a reasonable idea, I will go ahead and implement it and add a couple tests for it.

[eloyfelix]

Hi Greg, thanks for looking into this. Yes, it is definitely a good idea to do it.

[greglandrum]

Ok. I will try to get a PR done in the next couple days. As usual, writing the tests will be the majority of the effort. :-)

[eloyfelix]

done in #45