Added tests for optional argument (with null default value)
Added reordering of custom attributes in the test helper to fix test failures in ApprovedTests (see comment) + adapted asserted attributes order in SpecialClass(NoAssert).approved.txt
Changed handling of optional parameters:
* Parameter with null default value allows null values (existing behavior)
* Parameter with non-null default value adds argument null check
Added "MethodWithOptionalParameterWithNonNullDefaultValueButAllowNullAttribute" test case
Merge pull request #34 from ulrichb/ReorderCustomAttributesInTests

Reordering of custom attributes in the test assertions
Merge pull request #35 from ulrichb/OptParamWithNonNullDefaultValue

Argument check for optional parameters with non-null default value