c++-util: Add helper to convert time to/from string

Change-Id: I7e9910747368c18c039fd28e2b1076843fc4419e
diff --git a/Makefile.am b/Makefile.am
index 375b49a..8a6aaf2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -135,7 +135,8 @@
   src/util/logging.cpp \
   src/util/logging.hpp \
   src/util/ndnd-id-fetcher.hpp \
-  src/util/string-helper.hpp
+  src/util/string-helper.hpp \
+  src/util/time.hpp
 
 libndn_cpp_la_LIBADD  = @OPENSSL_LIBS@ @OSX_SECURITY_LIBS@
 libndn_cpp_la_LDFLAGS = @OPENSSL_LDFLAGS@  @SQLITE3_LDFLAGS@ @BOOST_LDFLAGS@