Errors, Status, Doc, DB transforms, Sorted Join fix, XmlMap, nicer log, blessings.

- An error package now groups all exceptions
- Blessings has been added to requirements, and is used to display nicer statuses and logs (from Log)
- Inline documentation (minor)
- Fix database extract
- Fix SortedJoin merge order: STDIN now gets priority and override STDIN2 if a field is defined in both.
- Maps use .map() method name instead of .mapper(), which was inconsistent.
- Implements XmlMap in a simple and flexible way (uses ElementTree).