added power modes demo

demos/powermodes/main.c

@@ -0,0 +1,34 @@
+#include "ch.h"
+#include "hal.h"
+#include "glcd.h"
+
+static GLCDDriver GLCDD1;
+
+int main(void) {
+	halInit();
+	chSysInit();
+	
+	lcdInit(&GLCDD1);
+	lcdClear(Black);
+	lcdDrawString(100, 100, "Hello World", White, Black);
+
+	// wait two seconds to see current LCD content
+	chThdSleepSeconds(2);
+
+	// brings LCD to sleep mode
+	lcdSetPowerMode(sleepOn);
+
+	// wait two seconds to see current LCD content
+	chThdSleepSeconds(2);
+
+	// brings LCD back from sleep mode
+	// content displayed before gets displayed again
+	lcdSetPowerMode(sleepOff);
+
+	while (TRUE) {
+		
+		chThdSleepMilliseconds(200);	
+	}
+
+	return 0;
+}