Clarify guidance on SDE expression results

Agree.  Propose that we clarify by adding a bullet to the conformance requirement: Supplemental data element criteria expressions MAY be of any type, including lists Note that this means we also need to provide guidance on how list-valued (and tuple-valued) SDEs would be represented in the resulting MeasureReport. Example to be provided after vote. Also reword the original statement to say: CURRENT: The supplemental data element expressions are normally expected to return a single value when evaluated in the context of a member of the population. For example, patient-based measures would return the value of a supplemental data element for a given patient. However, there are cases where returning multiple elements for supplemental data would be useful. For example, collecting observations related to a particular condition. The intent of this conformance requirement is to simplify implementation of supplemental data collection, so care should be taken when using supplemental data elements that return multiple elements.   PROPOSED: The supplemental data element expressions can return a single value or list of values when evaluated in the context of a member of the population. For example, patient-based measures would return the value of a supplemental data element for a given patient. However, there are cases where returning multiple elements for supplemental data would be useful. For example, collecting observations related to a particular condition.