Add syntax checks to the deserializer

[ewoutkramer]

Currently the deserializer is mostly concerned about the happy path. Add code that does the same checks as the current SDK does:

Xml syntactic checks

• incorrect/empty namespace . P, R:namespace ignored
• empty attributes . P, R: whitespace,null then value=null
• no attribute, no elements P ->S, R:empty child list, value=null SKIP?
• repeating elements inconsecutively P,->S
• Invalid FHIR Xhtml P ->T
• container resources with attributes . P, R:no contained found
• contained resources with attributes . P, R:no contained found
• container resources with multiple children . P, R:no contained found

Json syntactic checks

• incorrect use of null P, R: skip
• incorrect use/combinations of name and _name . P, R: return main
• incorrect use of arrays for name and _name . P, R:return main
• invalid json token type . P: skip unless some useful content found
• empty string values ->T, p:return null
• non-arrays with null values . P, R:return null
• empty objects . P, R:return null
• obsolete fhir_comments use . P, R:skip

[ewoutkramer]

For completeness, I'll add the semantic checks done in subsequent phases in the SDK:

Type checks

• complex nodes with values ->T
• unparseable primitive values .
• incorrect primitive value ->T
• NEW empty string in primitive value ->T
• NEW no value and no children ->T
• missing/superfluous contained resources ->T
• element names missing suffix for choice types .
• choice types with incorrect type ->T

for xml:

• elements out of order ->T
• incorrect use of xml nodes (attributes instead of elements) .

for json:

• missing/superfluous use of arrays .
• invalid xml in narrative ->T
• Invalid FHIR Xhtml in narrative ->T

[ewoutkramer]

While discussing this: we could decide which of these errors need to be configurable. Or we could actually allow a callback so the user can decide what to do with the errors or even insert correction logic.

[ewoutkramer]

I forgot one semantic check that is currently not done: all elements of an array should be of the same type.