No more irrelevant compiler warnings :-)

Added a "#pragma GCC diagnostic push/ignored/pop" around unsupported API functions, to avoid compiler warnings.

LiquidCrystal_I2C.cpp

@@ -311,6 +311,8 @@ void LiquidCrystal_I2C::printstr(const char c[]){
 
 
 // unsupported API functions
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
 void LiquidCrystal_I2C::off(){}
 void LiquidCrystal_I2C::on(){}
 void LiquidCrystal_I2C::setDelay (int cmdDelay,int charDelay) {}
@@ -320,5 +322,5 @@ uint8_t LiquidCrystal_I2C::init_bargraph(uint8_t graphtype){return 0;}
 void LiquidCrystal_I2C::draw_horizontal_graph(uint8_t row, uint8_t column, uint8_t len,  uint8_t pixel_col_end){}
 void LiquidCrystal_I2C::draw_vertical_graph(uint8_t row, uint8_t column, uint8_t len,  uint8_t pixel_row_end){}
 void LiquidCrystal_I2C::setContrast(uint8_t new_val){}
-
+#pragma GCC diagnostic pop