moving calendar to cowd, CowDbML

With calendar now little more than a b-tree, I am thinking that it should be moved down into CowDb--it is entirely usable at that level. COODBMS then stays tightly forcused on organizational structures specific to Rolons.

Also, for JOODBMS we need a notation which allows us to add transactional Rolons to the database. For this a simple XML markup language, CowDbML, would do the trick. This naturally extends into a logical block (like PByte or PSerializable). Note that since we already have a factory driven by type strings, the type string simply becomes the element name in the markup language. But we will need to change the type constants to be something a bit more readable.