3.2.0: sync with 3.1.1

[ralfhandl]

Remaining changes to 3.1.1

• 3.1.1 port of Move complex Sec Req example to appendix F #4091
• Port of last-minute 3.0.4 changes to 3.1.1 #4088
• 3.1.1: align format-markdown.sh with v3.0.4-dev #4085
• Markdown links are API Description, not API URLs #4079
• 3.1.1: port the undisputed parts of #2140 #4071
• 3.1.1: absent, empty, or incomplete security list #4064
• 3.1.1: tables cleanup #4056
• 3.1.1: example for "raw JSON" as message body #4055
• "Object" definition, etc. (3.1.1 port of #4050) #4052
• Clarify data model types and formats #4045
• 3.1.1: link to examples on learn site #4044
• markdownlint for 3.1.1.md #4041

Depends on and includes

• 3.2.0: replace "property" with "field" or "keyword" where appropriate #4035

Fixes #3938

[ralfhandl]

Added latest updates to 3.1.1

[handrews]

@ralfhandl if we follow the proposal in #3677 (comment), we will not need this PR as we will just abandon v3.2.0-dev in favor of a reconstructed v3.2-dev (there have only been four 3.2-specific changes so far, and porting those makes for a much nicer 3.2 version history!)

[ralfhandl]

@handrews Thanks for taking over!