Add NTAttribute including builder

src/Makefile

@@ -19,6 +19,7 @@ INC += ntmatrix.h
 INC += ntenum.h
 INC += ntunion.h
 INC += ntaggregate.h
+INC += ntattribute.h
 
 LIBSRCS += ntutils.cpp
 LIBSRCS += ntfield.cpp
@@ -33,6 +34,7 @@ LIBSRCS += ntmatrix.cpp
 LIBSRCS += ntenum.cpp
 LIBSRCS += ntunion.cpp
 LIBSRCS += ntaggregate.cpp
+LIBSRCS += ntattribute.cpp
 
 LIBRARY = nt