message: Fix endianness check in command.cpp.
  Somehow (bad merge?) the LITTLE_ENDIAN macro was never defined, so the
  old code didn't work.
  Detect endianness with macros defined by GCC.  See all macros by
  running:
  ~/.platformio/packages/toolchain-atmelavr/bin/avr-g++ -mmcu=atmega328p -dM -E -x c++ - < /dev/null
diff: @@ -15,7 +15,10 @@ limitations under the License.
  #include "command.h"
  +// Converts 4 bytes of big-endian data into a float.
  static float convIntTofloat(char *data);
  +
  +// Converts a float into 4 bytes of big-endian data.
  static uint32_t convfloatToInt(float float_value);
  void command_execute(enum command cmd, char *dataTx, uint8_t lenTx,
  @@ -164,16 +167,15 @@ void command_responseSend(uint8_t cmd, char *packet, uint8_t len) {
  }
  static float convIntTofloat(char *data) {
  -
  float f;
  -#ifdef LITTLE_ENDIAN
  +#ifndef __FLOAT_WORD_ORDER__
  +#error "Your compiler isn't defining the __FLOAT_WORD_ORDER__ macro?"
  +#elif __FLOAT_WORD_ORDER__ == __ORDER_LITTLE_ENDIAN__
  /* Convert big endian integer to little endian float */
  - uint32_t data_bEndian = 0;
  - uint32_t data_lEndian = 0;
  -
  + uint32_t data_bEndian;
  memcpy(&data_bEndian, data, sizeof(data_bEndian));
  - data_lEndian = __builtin_bswap32(data_bEndian);
  + uint32_t data_lEndian = __builtin_bswap32(data_bEndian);
  memcpy(&f, &data_lEndian, sizeof(f));
  #else
  /* Convert big endian to big endian float */
  @@ -184,19 +186,16 @@ static float convIntTofloat(char *data) {
  }
  static uint32_t convfloatToInt(float float_value) {
  -
  - #ifdef LITTLE_ENDIAN
  +#ifndef __FLOAT_WORD_ORDER__
  +#error "Your compiler isn't defining the __FLOAT_WORD_ORDER__ macro?"
  +#elif __FLOAT_WORD_ORDER__ == __ORDER_LITTLE_ENDIAN__
  /* Convert float into big endian format for transmission */
  - uint32_t data_bEndian = 0;
  - uint32_t data_lEndian = 0;
  -
  + uint32_t data_lEndian;
  memcpy(&data_lEndian, &float_value, sizeof(data_lEndian));
  - data_bEndian = __builtin_bswap32(data_lEndian);
  - return data_bEndian;
  + return __builtin_bswap32(data_lEndian);
  #else
  /* Keep float in big endian format */
  uint32_t data_bEndian;
  -
  memcpy(&data_bEndian, &float_value, sizeof(data_bEndian));
  return data_bEndian;
  #endif
  