ArduinoJson 6.21.2

* Fix compatibility with the Zephyr Project (issue bblanchon#1905)
* Allow using PROGMEM outside of Arduino (issue bblanchon#1903)
* Set default for `ARDUINOJSON_ENABLE_PROGMEM` to `1` on AVR

ArduinoJson 6.21.1

* Double speed of `DynamicJsonDocument::garbageCollect()`
* Fix compatibility with GCC 5.2 (issue bblanchon#1897)

ArduinoJson 6.21.0

* Drop support for C++98/C++03. Minimum required is C++11.
* Remove `ARDUINOJSON_NAMESPACE`; use `ArduinoJson` instead.
* Make string support generic (issue bblanchon#1807)

ArduinoJson 6.20.1

* Remove explicit exclusion of `as<char*>()` and `as<char>()` (issue bblanchon#1860)

ArduinoJson 6.20.0

* Add `JsonVariant::shallowCopy()` (issue bblanchon#1343)
* Fix `9.22337e+18 is outside the range of representable values of type 'long'`
* Fix comparison operators for `JsonArray`, `JsonArrayConst`, `JsonObject`, and `JsonObjectConst`
* Fix lax parsing of `true`, `false`, and `null` (issue bblanchon#1781)
* Remove undocumented `accept()` functions
* Rename `addElement()` to `add()`
* Remove `getElement()`, `getOrAddElement()`, `getMember()`, and `getOrAddMember()`
* Remove undocumented `JsonDocument::data()` and `JsonDocument::memoryPool()`
* Remove undocumented `JsonArrayIterator::internal()` and `JsonObjectIterator::internal()`
* Rename things in `ARDUINOJSON_NAMESPACE` to match the public names
* Add documentation to most public symbols
* Remove support for naked `char` (was deprecated since 6.18.0)

ArduinoJson 6.19.4

* Add `ElementProxy::memoryUsage()`
* Add `MemberProxy::memoryUsage()` (issue bblanchon#1730)
* Add implicit conversion from `JsonDocument` to `JsonVariant`
* Fix comparisons operators with `const JsonDocument&`

ArduinoJson 6.19.3

* Fix `call of overloaded 'String(const char*, int)' is ambiguous`
* Fix `JsonString` operator `==` and `!=` for non-zero-terminated string
* Fix `-Wsign-conversion` on GCC 8 (issue bblanchon#1715)
* MessagePack: serialize round floats as integers (issue bblanchon#1718)

ArduinoJson 6.19.2

* Fix `cannot convert 'pgm_p' to 'const void*'` (issue bblanchon#1707)

ArduinoJson 6.19.1

* Fix crash when adding an object member in a too small `JsonDocument`
* Fix filter not working in zero-copy mode (issue bblanchon#1697)

ArduinoJson 6.19.0

* Remove `ARDUINOJSON_EMBEDDED_MODE` and assume we run on an embedded platform.