* Reimplement value() access functions
* Merges the 'const char *' with the 'ValueType &&' overloads.
* Fixes ambiguities when default value is 0.
* Fixes 'no matching function' error when specifying ValueType template
parameter.
* Fixes incorrect template parameter order in previous overloads.
* Add additional value() tests
* Make JSON_MultipleHeaders visible to unit tests
Define the macro JSON_TEST_USING_MULTIPLE_HEADERS to 0/1 depending on
JSON_MultipleHeaders.
* Add type_traits unit test
* Update documentation
* Move UDLs into nlohmann::literals::json_literals namespace
* Add 'using namespace' to unit tests
* Add 'using namespace' to examples
* Add 'using namespace' to README
* Move UDL mkdocs pages out of basic_json/
* Update documentation
* Update docset index
* Add JSON_GlobalUDLs CMake option
* Add unit test
* Build examples without global UDLs
* Add CI target
* Add overloads for more key types to ordered_map
Add overloads to accept additional key types defined by type trait
detail::is_usable_as_key_type to ordered_map.
The same key types that can be used with json can now also be used with
ordered_json.
* Fix ordered_map::erase(first, last) with first == last
* Modify element access unit test to also test ordered_json
