Allow compiling and using as DLL in windows (#502)

* printf.h fixed to compile clean - need to check whether this is the right
thing to do

* fix warnings and errors in test compiles with BUILD_SHARED_LIBS

* did requested changes and added one change to allow all tests to succeed
in windows DLL

test/time-test.cc

@@ -6,6 +6,9 @@
 
  For the license information refer to format.h.
  */
+#ifdef WIN32
+#define _CRT_SECURE_NO_WARNINGS
+#endif
 
 #include "gmock/gmock.h"
 #include "fmt/time.h"