More documentation updates for 3.11.0 (#3553)

* mkdocs: add string_view examples

* mkdocs: reference underlying operators

* mkdocs: add operator<=> examples

* mkdocs: fix style check issues

* mkdocs: tweak BJData page

* mkdocs: add CMake option hints to macros

* mkdocs: fix JSON_DISABLE_ENUM_SERIALIZATION definition

* mkdocs: fix link to unit-udt.cpp

* mkdocs: fix "Arbitrary Type Conversions" title

* mkdocs: link to api/macros/*.md instead of features/macros.md

* mkdocs: document JSON_DisableEnumSerialization CMake option

* mkdocs: encode required C++ standard in example files

* docset: detect gsed/sed

* docset: update index

* docset: fix CSS patching

* docset: add list_missing_pages make target

* docset: add list_removed_paths make target

* docset: replace page titles with name from index

* docset: add install target for Zeal docset browser

* Use GCC_TOOL in ci_test_documentation target

docs/mkdocs/docs/api/basic_json/count.md

@@ -44,18 +44,32 @@ This method always returns `0` when executed on a JSON type that is not an objec
 
 ## Examples
 
-??? example
+??? example "Example: (1) count number of elements"
 
     The example shows how `count()` is used.
     
     ```cpp
-    --8<-- "examples/count.cpp"
+    --8<-- "examples/count__object_t_key_type.cpp"
     ```
     
     Output:
     
     ```json
-    --8<-- "examples/count.output"
+    --8<-- "examples/count__object_t_key_type.output"
+    ```
+
+??? example "Example: (2) count number of elements using string_view"
+
+    The example shows how `count()` is used.
+    
+    ```cpp
+    --8<-- "examples/count__keytype.c++17.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/count__keytype.c++17.output"
     ```
 
 ## Version history