Add operator/= and operator/ to construct a JSON pointer by appending two JSON pointers

Fix gcc9 build error test/src/unit-allocator.cpp (Issue #1472)

Use C++11 features supported by CMake 3.1.

Update Buckaroo instructions in README.md

fix GCC 7.1.1 - 7.2.1 on CentOS

closes https://github.com/nlohmann/json/issues/670

 * Updates Buckaroo instructions to v2

Rename private json_pointer::is_root as public json_pointer::empty for consistency with std::filesystem::path

Fix typo in README.md

Fixes https://github.com/nlohmann/json/issues/1486.

Implement contains() member function

Fix documentation

Remove two instance of duplicate paragraphs.

Disable Clang -Wmismatched-tags warning on tuple_size / tuple_element

Disable installation when used as meson subproject. #1463

Add operator/= and operator/ to construct a JSON pointer by appending two JSON pointers, as well as convenience op/= and op= to append a single unescaped token or array index; inspired by std::filesystem::path

remove extra semicolon from readme

docs: README typo

Just another small typo I found in the README.

in example of NLOHMANN_JSON_SERIALIZE_ENUM

Closes #1447.

attempt to fix #1445, flush buffer in serializer::dump_escaped in UTF8_REJECT case.