case format for type element in Choice Types

[niquola]

We represent choice types as records, the question is what case to use to name type-elements

1. Observation.value.quantity - all elements in FHIR starts from lower
2. Observation.value.Quantity - keep exact type name

[niquola]

in (1) we could not get exact type name just from element name, because we do not know was first letter of type name up or down

[niquola]

We need clarification in spec about this!
And fix example from https://github.com/rbrush/sql-on-fhir/blob/master/sql-on-fhir.md#extensions-duplicated-as-first-class-fields, which is lowercase

[rbrush]

I think the "least surprising behavior" for this is that all fields are lower camelCase, so it would be Observation.value.quantity. Thinking about the perspective of a user new to the system, I'd imagine they'd expect it to be lower case do I'd lean that way...but could be convinced otherwise if there is a compelling reason.