Allow initialization of single values when quantity is 0..1 about fhir_models

[radamson]

Thanks for reporting this issue/suggestion and sorry for the delay in responding to this!

I think the suggestion makes sense and is something we should support in the library (without having to resort to wrapping it in an Array or jumping through other hoops).

Currently the library will "inflate" these complex elements if they are provided as a simple Hash. e.g.

range = FHIR::Range.new(low: {value: 18})
range.valid? # => true

Wrapping an element which should have a cardinality of 0..1 in an Array is undesirable and as such I'm not too keen on the second possibility.