Require user to request access to millisecond

Readme.md

@@ -53,7 +53,8 @@ year(t); // the year for the given time t
 There are also two functions that return the number of milliseconds left-over. Care
 should be taken when using this value since there are no functions to set the time
 with sub-second accuracy and the value may jump when the time is synchronized.
-However, it is always consistent with the current time.
+However, it is always consistent with the current time. To access these functions,
+you have to `#define TIMELIB_ENABLE_MILLIS` in your sketch.
 
 ```c
 time_t t = now(uint32_t& m) // store the current time in time variable t and milliseconds in m

Time.cpp

@@ -33,6 +33,7 @@
 #include <WProgram.h> 
 #endif
 
+#define TIMELIB_ENABLE_MILLIS
 #include "TimeLib.h"
 
 static tmElements_t tm; // a cache of time elements

TimeLib.h

@@ -108,7 +108,9 @@ int minute(); // the minute now
 int minute(time_t t); // the minute for the given time
 int second(); // the second now 
 int second(time_t t); // the second for the given time
+#ifdef TIMELIB_ENABLE_MILLIS
 int millisecond(); // the millisecond now
+#endif
 int day(); // the day now 
 int day(time_t t); // the day for the given time
 int weekday(); // the weekday now (Sunday is day 1) 
@@ -119,7 +121,9 @@ int year(); // the full four digit year: (2009, 2010 etc)
 int year(time_t t); // the year for the given time
 
 time_t now(); // return the current time as seconds since Jan 1 1970 
+#ifdef TIMELIB_ENABLE_MILLIS
 time_t now(uint32_t& sysTimeMillis); // return the current time as seconds and milliseconds since Jan 1 1970
+#endif
 void setTime(time_t t);
 void setTime(int hr,int min,int sec,int day, int month, int yr);
 void adjustTime(long adjustment);