Redirects Logger.Log(a, b, ex) to Logger.LogException(a, b, ex)

Fixes issue #91, for method signatures `Log<TArgument>(LogLevel, string, TArgument)` where `TArgument` is of base type `Exception`, along with related helper methods.

Another candidate for this is `Log(LogLevel, string, object)` where object is an `Exception`, and there may also be others. Please let me know if you would like these added.

As this is a behaviour change (although I think this would be viewed as expected) - perhaps a mention should be made in the next release notes? Or even a config option?