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/api/macros/index.md

@@ -0,0 +1,18 @@
+# Macros
+
+Some aspects of the library can be configured by defining preprocessor macros before including the `json.hpp` header.
+
+- [`JSON_ASSERT(x)`](json_assert.md)
+- `JSON_CATCH_USER(exception)`
+- `JSON_DIAGNOSTICS`
+- `JSON_HAS_CPP_11`, `JSON_HAS_CPP_14`, `JSON_HAS_CPP_17`, `JSON_HAS_CPP_20`
+- `JSON_NOEXCEPTION`
+- `JSON_NO_IO`
+- `JSON_SKIP_UNSUPPORTED_COMPILER_CHECK`
+- `JSON_THROW_USER(exception)`
+- `JSON_TRY_USER`
+- `JSON_USE_IMPLICIT_CONVERSIONS`
+- `NLOHMANN_DEFINE_TYPE_INTRUSIVE(type, member...)`
+- `NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(type, member...)`
+- `NLOHMANN_JSON_SERIALIZE_ENUM(type, ...)`
+- `NLOHMANN_JSON_VERSION_MAJOR`, `NLOHMANN_JSON_VERSION_MINOR`, `NLOHMANN_JSON_VERSION_PATCH`

doc/mkdocs/docs/api/macros/json_assert.md

@@ -0,0 +1,11 @@
+# JSON_ASSERT(x)
+
+```cpp
+JSON_ASSERT(x)
+```
+
+## Default implementation
+
+```cpp
+assert(x);
+```