doc: unify more headings

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• documentation is changed or added
• commit message follows commit guidelines

• Unify punctuation.
• Unify case.
• Unify format nits (add new for a constructor, remove () from a class name).
• Unify backticks. We usually do not wrap headings in backticks if these headings contain only API properties or function signatures. In such cases, backticks break uniformity, reduce font size in TOC and headings and baffle doctools.

Also in passing:

• Fix a typo.
• Add a type.