istream& replaced by OIOin&

The type of the first (and now only) argument to the constructors called by readFrom(istream&) has been changed from an istream& to an OIOin&. This avoids naming conflicts with other constructors. Also, OIOin is an abstract base class, and all input operators are virtual functions, so you can customize the Object I/O format by defining your own derived classes. OIOistream and OIOnihin implement a format similar to the old OOPS format.