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/examples/parse__contiguouscontainer__parser_callback_t.cpp

@@ -7,7 +7,7 @@ using json = nlohmann::json;
 int main()
 {
     // a JSON text given as std::vector
-    std::vector<uint8_t> text = {'[', '1', ',', '2', ',', '3', ']', '\0'};
+    std::vector<std::uint8_t> text = {'[', '1', ',', '2', ',', '3', ']', '\0'};
 
     // parse and serialize JSON
     json j_complete = json::parse(text);