Fixes to documentation-main.html, so that section headings work and look the same.

The main documentation page has very good content. But there were some problems with a few of the links in the Table of Contents (anchor collisions), and not all of the section heading formatting was consistent.

Firstly, this PR fixes the Table of Contents link collision problems. Some links were going to the incorrect section due to attribute name collisions. (See commit message for details).

Secondly, this PR fixes the section heading formatting inconsistencies (as well as missing appropriate HTML tags for headings).

Thirdly, this PR adjusts some of the formatting of the HTML file itself so that all of the section headings have a similar HTML format (so that the file is easier to work with). 

See file changes and commit messages for details.