Clearer documentation on all Resource classes and their constructors

### Do you want to request a feature, report a bug, or improve documentation?

### If you are reporting a bug?

**What is the current behavior?**

**What is the expected behavior?**

**What are the steps to reproduce?**

**What OS are you using and what version of node.js and @asymmetrik/node-fhir-server-core are you running?**
