SDCARDDETECT -> SD_DETECT, added docs

- `SD_DETECT_PIN` replaces `SDCARDDETECT`
- `SD_DETECT_INVERTED` replaces `SDCARDDETECTINVERTED`
- Revise the description of `SD_DETECT_INVERTED`
- Add a note about the override of `SD_DETECT_INVERTED` in
`Conditionals.h`

Marlin/example_configurations/RigidBot/Configuration.h

@@ -649,7 +649,7 @@ const bool Z_PROBE_ENDSTOP_INVERTING = false; // set to true to invert the logic
 //
 // ==> REMEMBER TO INSTALL U8glib to your ARDUINO library folder: http://code.google.com/p/u8glib/wiki/u8glib
 //#define ELB_FULL_GRAPHIC_CONTROLLER
-//#define SDCARDDETECTINVERTED
+//#define SD_DETECT_INVERTED
 
 // The RepRapDiscount Smart Controller (white PCB)
 // http://reprap.org/wiki/RepRapDiscount_Smart_Controller

Marlin/example_configurations/RigidBot/Configuration_adv.h

@@ -292,11 +292,11 @@
 #if ENABLED(SDSUPPORT)
 
   // If you are using a RAMPS board or cheap E-bay purchased boards that do not detect when an SD card is inserted
-  // You can get round this by connecting a push button or single throw switch to the pin defined as SDCARDCARDDETECT
+  // You can get round this by connecting a push button or single throw switch to the pin defined as SD_DETECT_PIN
   // in the pins.h file.  When using a push button pulling the pin to ground this will need inverted.  This setting should
   // be commented out otherwise
   #ifndef ELB_FULL_GRAPHIC_CONTROLLER
-    #define SDCARDDETECTINVERTED
+    #define SD_DETECT_INVERTED
   #endif
 
   #define SD_FINISHED_STEPPERRELEASE true  //if sd support and the file is finished: disable steppers?