Merge branch 'ps/config-subcommands' into ps/builtin-config-cleanup

* ps/config-subcommands: builtin/config: display subcommand help builtin/config: introduce "edit" subcommand builtin/config: introduce "remove-section" subcommand builtin/config: introduce "rename-section" subcommand builtin/config: introduce "unset" subcommand builtin/config: introduce "set" subcommand builtin/config: introduce "get" subcommand builtin/config: introduce "list" subcommand builtin/config: pull out function to handle `--null` builtin/config: pull out function to handle config location builtin/config: use `OPT_CMDMODE()` to specify modes builtin/config: move "fixed-value" option to correct group builtin/config: move option array around config: clarify memory ownership when preparing comment strings