anchors for sections of ontology description; TOC refinements

[VladimirAlexiev]

Related to #126

You handle Markdown headings in ontology description (thanks!), eg see this screen from http://rawgit2.com/euBusinessGraph/eubg-data/master/ontology/doc.html (euBusinessGraph/eubg-data#18)

Please also:

• Move the TOC above Overview because good ontologies have long overviews, and a TOC should be before the main body of text
• include the extra sections as headings in the TOC
• generate github-like anchors for these headings, eg _registered_organization_company for "Registered organization (company)"
• Use bulleted list rather than numbered list for the TOC because your document sections are not numbered.

So overall, it should look like this:

---

euBusinessGraph ontology

...
Code Repository
https://github.com/euBusinessGraph/eubg-data

Table of Contents

• Overview
  • Registered Organization (company)
  • Identifier System
  • Officer
  • Dataset Descriptions
• Classes
• Object Properties
• Datatype Properties
• Namespaces
• Legend

Overview

...

Registered Organization (company)

...