Merge pull request #1 from Elwell/master

trivial change to declare PROGMEM as const

Author: jcw

RTClib.cpp

@@ -16,7 +16,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 // utility code, some of this could be exposed in the DateTime API if needed
 
-static uint8_t daysInMonth [] PROGMEM = { 31,28,31,30,31,30,31,31,30,31,30,31 };
+static const uint8_t daysInMonth [] PROGMEM = { 31,28,31,30,31,30,31,31,30,31,30,31 };
 
 // number of days since 2000/01/01, valid for 2001..2099
 static uint16_t date2days(uint16_t y, uint8_t m, uint8_t d) {