Changed argument type

@gergelytakacs error() and serialPrint() functions sometimes throw a warning message: "ISO C++ forbids converting a string constant to 'char*'" when used like they were meant to - serialPrint("text"). Sketch is compilable even without this change, this is just to satisfy the compiler by using the "more correct" argument type.

src/AutomationShield.cpp

@@ -34,7 +34,7 @@ byte AutomationShieldClass::percToPwm(float perc){
 	return byte(percFloat);
 }
 
- void AutomationShieldClass::error(char *str) // Error handler function
+ void AutomationShieldClass::error(const char *str) // Error handler function
  {
  #if ECHO_TO_SERIAL                      // If Serial Echo is turned on in the DEFINE (by advanced user)
  Serial.print("\nError: ");
@@ -44,7 +44,7 @@ byte AutomationShieldClass::percToPwm(float perc){
  while (1);                              // Stop all activity in busy cycle, so user definitely knows what's wrong.
  }
 
- void AutomationShieldClass::serialPrint(char *str){   // Function for printing messages to serial monitor if its enabled
+ void AutomationShieldClass::serialPrint(const char *str){   // Function for printing messages to serial monitor if its enabled
  #if ECHO_TO_SERIAL                                    // If Serial Echo is turned on in the DEFINE (by advanced user)
  Serial.print(str);                                    // Print message to serial monitor
  #endif 

src/AutomationShield.h

@@ -43,8 +43,8 @@
  class AutomationShieldClass{   
   public:    
     float mapFloat(float x, float in_min, float in_max, float out_min, float out_max);
-    void error(char *str);
-    void serialPrint(char *str);
+    void error(const char *str);
+    void serialPrint(const char *str);
     float constrainFloat(float x, float min_x, float max_x); 
     byte percToPwm(float perc); 
 }; // end of the class