Minor performance improvements for ESP32

Remove legacy changes for double buffered SPI
Eliminate unecessary ESP32 SPI read/modify write
Eliminate two stage control bit changes (may impact some diplays with
setup/hold  timing and show ESP32 hardware register bug?)
Add single register write for CS and DC command
Make setAddrWindow smarter (as used in previous AVR library)
Improve compatibility with GFX sketches
Re-arrange comments slightly to improve positioning

Extensions/Smooth_font.cpp

@@ -78,6 +78,12 @@ void TFT_eSPI::loadFont(String fontName)
     
   _gFontFilename = "/" + fontName + ".vlw";
 
+  // Avoid a crash on the ESP32 if the file does not exist
+  if (SPIFFS.exists(_gFontFilename) == false) {
+    Serial.println("Font file " + fontName + " not found!");
+    return;
+  }
+
   fontFile = SPIFFS.open( _gFontFilename, "r");
 
   if(!fontFile) return;
@@ -479,7 +485,6 @@ void TFT_eSPI::drawGlyph(uint16_t code)
 void TFT_eSPI::showFont(uint32_t td)
 {
   if(!fontLoaded) return;
-//  fontFile = SPIFFS.open( _gFontFilename, "r" );
 
   if(!fontFile)
   {