As requested by Dr. Andrew C.R. Martin

Note that this version is probably identical to two versions ago.

Add extra include file for aix to find endian information.

 including arguments allowed.

 having to modify the system-wide library database.

Define constants to allow day of week decoding.
Add new datetime and timespan routines.

Remove older date and time code (retain NEW_DATE_CODE and NEW_TIME_CODE).
Use common encoder for date and time.
Fix datetime +/- timespan math bug.