Clean up TimeVal and TimeValDifference classes so that each can access
the other.

o) Clean up subrecord I/O to make it more user-friendly
o) Write smallerThan method to compare with number of bytes
o) Clean up RcdReader and RcdWriter to pay more attention to errors; also
   check Dmy works and do OnlWriterAsc


Should the following go into a new rio package?
o) Write merger/demerger for records
o) Override "lasi in is only one out" buffer for records
o) Override sockets for shorter records than RcdArena
o) Move OnlWriter to RioWriter?
