Improvement of specimen description

[hackermd]

This PR introduces the following changes:

• Additional checks to ensure that processing_type and processing_procedure match
• Support for staining substances specified as text
• New SpecimenProcessing class to describe specimen processing

[hackermd]

Very unfamiliar with this part of the standard, but why does the processing_type even need to be passed if it's determined by the type of the processing_procedure?

You are right, it's not really required. I realized that having the two parameters (processing_type and processing_procedure) is error prone and therefore added checks to ensure that the arguments match. We could now deprecate processing_type. However, since it's currently the first parameter, we would break the API even if we would make it optional for the purpose of deprecation (since we would need to move the parameter). Thoughts?

[CPBridge]

Hmm, I'd be tempted to deprecate as gracefully as we can as we are still pre 1.0 but I defer to your judgement

[hackermd]

@CPBridge I deprecated the parameter and added a paragraph to the release notes (f8ddb989aa039c2944b2746eff46f4f84660eae7).