Change SDA/SCL from uint8_t to int (#348)

This allows to assign `-1` to skip the call to `begin()`.

Author: mengguang

src/SH1106Wire.h

@@ -43,8 +43,8 @@
 class SH1106Wire : public OLEDDisplay {
   private:
       uint8_t             _address;
-      uint8_t             _sda;
-      uint8_t             _scl;
+      int             _sda;
+      int             _scl;
       bool                _doI2cAutoInit = false;
       TwoWire*            _wire = NULL;
       int                 _frequency;
@@ -65,7 +65,7 @@ class SH1106Wire : public OLEDDisplay {
      * @param _i2cBus on ESP32 with 2 I2C HW buses, I2C_ONE for 1st Bus, I2C_TWO fot 2nd bus, default I2C_ONE
      * @param _frequency for Frequency by default Let's use ~700khz if ESP8266 is in 160Mhz mode, this will be limited to ~400khz if the ESP8266 in 80Mhz mode
      */
-    SH1106Wire(uint8_t _address, uint8_t _sda, uint8_t _scl, OLEDDISPLAY_GEOMETRY g = GEOMETRY_128_64, HW_I2C _i2cBus = I2C_ONE, int _frequency = 700000) {
+    SH1106Wire(uint8_t _address, int _sda = -1, int _scl = -1, OLEDDISPLAY_GEOMETRY g = GEOMETRY_128_64, HW_I2C _i2cBus = I2C_ONE, int _frequency = 700000) {
       setGeometry(g);
 
       this->_address = _address;