doc: unify more headings

[vsemozhetbyt]

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.

[vsemozhetbyt]

CI-lite: https://ci.nodejs.org/job/node-test-pull-request-lite/526/

[trivikr]

More backticks need to be removed from headings under Implementation Considerations

[vsemozhetbyt]

@trivikr I've seen them, but abstained from deletion: these are not formal API sections, just extra notes about previously described API. The similar cases are these subsections:

https://github.com/nodejs/node/blob/master/doc/api/async_hooks.md#type
https://github.com/nodejs/node/blob/master/doc/api/async_hooks.md#triggerid
https://github.com/nodejs/node/blob/master/doc/api/async_hooks.md#resource

They describe parameters from the previous formal signature in more details.

All these should not be parsed by, say, JSON doctools as formal API parts, just as misc sections.

[vsemozhetbyt]

Landed in 6e869be