Filtering example is wrong

[benmcmorran]

The example test case filtering code does not compile. Specifically here:

var filterExpression = runContext.GetTestCaseFilter(supportedProperties, (propertyName) =>
{
    TestProperty testProperty = null;
    supportedProperties.TryGetValue(propertyName, out testProperty);
    return testProperty;
});

GetTestCaseFilter() has this signature:

ITestCaseFilterExpression GetTestCaseFilter(IEnumerable<String> supportedProperties, Func<string, TestProperty> propertyProvider);

but supportedProperties in the example is a Dictionary<string, TestProperty>