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

include/nlohmann/detail/input/input_adapters.hpp

@@ -104,7 +104,7 @@ class input_stream_adapter
 
     // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
     // ensure that std::char_traits<char>::eof() and the character 0xFF do not
-    // end up as the same value, eg. 0xFFFFFFFF.
+    // end up as the same value, e.g. 0xFFFFFFFF.
     std::char_traits<char>::int_type get_character()
     {
         auto res = sb->sbumpc();
@@ -450,7 +450,7 @@ auto input_adapter(T (&array)[N]) -> decltype(input_adapter(array, array + N)) /
 }
 
 // This class only handles inputs of input_buffer_adapter type.
-// It's required so that expressions like {ptr, len} can be implicitly casted
+// It's required so that expressions like {ptr, len} can be implicitly cast
 // to the correct adapter.
 class span_input_adapter
 {