Refactor OpenAPI Description Structure sections

* Remove "OpenAPI Description" and "OpenAPI Document" section
  headings and reorder those paragraphs and the intro
  "OpenAPI Description Structure" paragraph to define the terms inline
* Switch Appendixes F and G
    * F->G stays as-is, with base URI examples
    * G->F is expanded to a more general
      "Parsing and Resolution Guidance" section
* Move several pieces of "Parsing Documents" to Appendix G
    * How to parse complete documents as the intro section
    * A "Warnings Regarding Fragmentary Parsing" section
* Move "Structural Interoperability" under Appendix G and rename
  it to "Conflicts Between Field Types and Reference Contexts"
* Move most of "Resolving Implicit Connections to Appendix G and
  rename it "Guidance Regarding Implicit Connections"
    * Put the original Section F implicit connection examples as
      a "Implicit Connection Resolution Examples" subsection

Minimal adjustments were made to links to keep the build functional.

Author: handrews