add printf support to ESP32/8266 and arduino-pico cores (#873)

* add printf support to ESP* and arduino-pico cores
* add ESP32/8266 boards to PlatformIO CI

   Arduino CLI seems to have trouble getting the esp* core that
   corresponds to the fqbn prefix

.github/workflows/build_platformIO.yml

@@ -114,6 +114,8 @@ jobs:
  - "teensylc"
  - "genericSTM32F411CE"
  - "blackpill_f103c8"
+ - "nodemcuv2"
+ - "adafruit_qtpy_esp32s2"
 
  steps:
  - uses: actions/checkout@v2

RF24_config.h

@@ -159,12 +159,18 @@ extern HardwareSPI SPI;
  #endif // defined (__ARDUINO_X86__)
 
  // Progmem is Arduino-specific
- #if defined(ARDUINO_ARCH_ESP8266) || defined(ESP32)
+ #if defined(ARDUINO_ARCH_ESP8266) || defined(ESP32) || (defined(ARDUINO_ARCH_RP2040) && !defined(ARDUINO_ARCH_MBED))
  #include <pgmspace.h>
  #define PRIPSTR "%s"
  #ifndef pgm_read_ptr
  #define pgm_read_ptr(p) (*(void* const*)(p))
  #endif
+ // Serial.printf() is no longer defined in the unifying Arduino/ArduinoCore-API repo
+ // Serial.printf() is defined if using the arduino-pico/esp32/8266 repo
+ #if defined(ARDUINO_ARCH_ESP32) // do not `undef` when using the espressif SDK only
+ #undef printf_P // needed for ESP32 core
+ #endif
+ #define printf_P Serial.printf
  #elif defined(ARDUINO) && !defined(ESP_PLATFORM) && !defined(__arm__) && !defined(__ARDUINO_X86__) || defined(XMEGA)
  #include <avr/pgmspace.h>
  #define PRIPSTR "%S"