Add better exception message when 0000-00-00 can't be converted

[bgrainger]

When InvalidCastException("Unable to convert MySQL date/time to System.DateTime.") is thrown, add extra text to the exception message (and/or a troubleshooting documentation page) that explains how to solve the problem.

MySqlConnector/src/MySqlConnector/Core/TextRow.cs

Line 155 in 6e0b225

throw new InvalidCastException("Unable to convert MySQL date/time to System.DateTime.");

From DapperLib/Dapper#1323.

[bgrainger]

Fixed by #712.

[bgrainger]

Fixed in 0.60.0.