Exceptions not documented when opening a file

[jdh28]

It would be useful for methods like ExcelReaderFactory.CreateReader to document the possible exceptions that can be thrown.

For example, we had a corrupted .xlsx file that threw a System.IO.InvalidDataException, which surprisingly does not derive from IOException.

[jdh28]

I would be happy to submit a PR to fix this if it is wanted.

The simplest fix is to list all the possible exceptions, but actually, I think it would be more useful to catch at least some of the possible exceptions and wrap them in ExcelReaderException. But this is probably a breaking change.