Better exception message when parameter isn't supported

[bgrainger]

From PomeloFoundation/Pomelo.EntityFrameworkCore.MySql#1287 (comment)

As per #410 (comment), unsupported parameter value types cause a NotSupportedException to be thrown:

MySqlConnector/src/MySqlConnector/MySqlParameter.cs

Line 433 in 6413d13

throw new NotSupportedException("Parameter type {0} (DbType: {1}) not currently supported. Value: {2}".FormatInvariant(Value.GetType().Name, DbType, Value));

A documentation page explaining this in more detail should be created, and the exception message updated with a quick description of the solution (call .ToString()) and a link to the documentation.

[bgrainger]

Fixed in 1.3.0.