Support multiple sensors

[caternuson]

For #16 and maybe #18. Add support for multiple sensors. Sort of a hack, but tested and works. Basic idea is to add new class members for i2c_dev and spi_dev and then dynamically set them to the global ones for each read method.

Do not have BMP390 to test.

Multiple SPI Test

#include "Adafruit_BMP3XX.h"

#define BMP1_CS 7
#define BMP2_CS 9

Adafruit_BMP3XX bmp1;
Adafruit_BMP3XX bmp2;

void setup() {
  Serial.begin(115200);
  while (!Serial);
  Serial.println("Adafruit BMP388 / BMP390 test");

  if (! bmp1.begin_SPI(BMP1_CS)) {  // hardware SPI mode  
    Serial.println("Could not find a valid BMP sensor #1, check wiring!");
    while (1);
  }

  if (! bmp2.begin_SPI(BMP2_CS)) {  // hardware SPI mode  
    Serial.println("Could not find a valid BMP sensor #2, check wiring!");
    while (1);
  }

  Serial.println("Initialization Success!");
}

void loop() {
  if (! bmp1.performReading()) {
    Serial.println("Failed to perform reading BMP #1 :(");
    return;
  }
  Serial.print("BMP #1 Temperature = ");
  Serial.print(bmp1.temperature);
  Serial.println(" *C");

  if (! bmp2.performReading()) {
    Serial.println("Failed to perform reading BMP #2 :(");
    return;
  }
  Serial.print("BMP #2 Temperature = ");
  Serial.print(bmp2.temperature);
  Serial.println(" *C");

  delay(2000);
  
}

Multiple I2C Test

#include "Adafruit_BMP3XX.h"

Adafruit_BMP3XX bmp1;
Adafruit_BMP3XX bmp2;

void setup() {
  Serial.begin(115200);
  while (!Serial);
  Serial.println("Adafruit BMP388 / BMP390 test");

  if (! bmp1.begin_I2C()) {  
    Serial.println("Could not find a valid BMP sensor #1, check wiring!");
    while (1);
  }

  if (! bmp2.begin_I2C(0x76)) {  
    Serial.println("Could not find a valid BMP sensor #2, check wiring!");
    while (1);
  }

  Serial.println("Initialization Success!");
}

void loop() {
  if (! bmp1.performReading()) {
    Serial.println("Failed to perform reading BMP #1 :(");
    return;
  }
  Serial.print("BMP #1 Temperature = ");
  Serial.print(bmp1.temperature);
  Serial.println(" *C");

  if (! bmp2.performReading()) {
    Serial.println("Failed to perform reading BMP #2 :(");
    return;
  }
  Serial.print("BMP #2 Temperature = ");
  Serial.print(bmp2.temperature);
  Serial.println(" *C");

  delay(2000);
  
}

Both work and print out expected results. Can breathe on second sensor and see its temp value rise.