Dot star spi fixes (#249)

* Update DotStarSpiMethod.h

fixes for SPI.transfer
updated to modern beginTransaction

* Update DotStarSpiMethod.h

Use beginTransaction as this is the most modern way to use the SPI
AVR loops and sends one byte at a time since they don't have a method that doesn't overwrite the out buffer like esp does

src/internal/DotStarSpiMethod.h

@@ -55,24 +55,33 @@ public:
     void Initialize(int8_t sck, int8_t miso, int8_t mosi, int8_t ss)
     {
         SPI.begin(sck, miso, mosi, ss);
-        init();
     }
 #endif
 
     void Initialize()
     {
         SPI.begin();
-        init();
     }
 
     void Update()
     {
-        // due to API inconsistencies need to call different methods on SPI
+        SPI.beginTransaction(SPISettings(20000000L, MSBFIRST, SPI_MODE0));
 #if defined(ARDUINO_ARCH_ESP8266) || defined(ARDUINO_ARCH_ESP32)
+        // ESPs have a method to write without inplace overwriting the send buffer
+        // since we don't care what gets received, use it for performance
         SPI.writeBytes(_sendBuffer, _sizeSendBuffer);
+
 #else
-        SPI.transfer(_sendBuffer, _sizeSendBuffer);
+        // default ARDUINO transfer inplace overwrites the send buffer
+        // which is bad, so we have to send one byte at a time
+        uint8_t* out = _sendBuffer;
+        uint8_t* end = out + _sizeSendBuffer;
+        while (out < end)
+        {
+            SPI.transfer(*out++);
+        }
 #endif
+        SPI.endTransaction();
     }
 
     uint8_t* getPixels() const
@@ -92,21 +101,6 @@ private:
 
     uint8_t* _sendBuffer;       // Holds SPI send Buffer, including LED color values
 
-    void init()
-    {
-#if defined(ARDUINO_ARCH_ESP8266) 
-        SPI.setFrequency(4000000L); // more than 4mhz causes CLK pulse malformation
-#elif defined(ARDUINO_ARCH_ESP32)
-        SPI.setFrequency(4000000L); // more than 4mhz causes CLK pulse malformation
-#elif defined(ARDUINO_ARCH_AVR) 
-        SPI.setClockDivider(SPI_CLOCK_DIV2); // 8 MHz (6 MHz on Pro Trinket 3V)
-#else
-        SPI.setClockDivider((F_CPU + 4000000L) / 8000000L); // 8-ish MHz on Due
-#endif
-        SPI.setBitOrder(MSBFIRST);
-        SPI.setDataMode(SPI_MODE0);
-    }
-
     size_t calcBufferSize(size_t sizePixels) const
     {
         const size_t countEndFrameBytes = calcEndFrameSize(sizePixels);