Consolidate documentation (#3071)

* 🔥 consolidate documentation
* ♻️ overwork std specializations
* 🚚 move images files to mkdocs
* ♻️ fix URLs
* 🔧 tweak MkDocs configuration
* 🔧 add namespaces
* 📝 document deprecations
* 📝 document documentation generation
* 🚸 improve search
* 🚸 add examples
* 🚧 start adding documentation for macros
* 📝 add note for https://github.com/nlohmann/json/issues/874#issuecomment-1001699139
* 📝 overwork example handling
* 📝 fix Markdown tables

doc/mkdocs/docs/integration/pkg-config.md

@@ -6,7 +6,7 @@ If you are using bare Makefiles, you can use `pkg-config` to generate the includ
 pkg-config nlohmann_json --cflags
 ```
 
-Users of the [Meson build system](package_managers.md#meson) will also be able to use a system wide library, which will be found by `pkg-config`:
+Users of the [Meson build system](package_managers.md#meson) will also be able to use a system-wide library, which will be found by `pkg-config`:
 
 ```meson
 json = dependency('nlohmann_json', required: true)