[Dev] new xml-less item persistence

[Andi Vajda]

I just checked in a complete rewrite of value serialization that does not 
involve any XML. The performance improvements are significant both for item 
saving and item loading. On my mac, a 1Ghz 1Gb powerbook G4:

   - first commit from scratch is down to 13s from 18s
   - Chandler startup time from an existing repository is also down to 13s from
     about 18s (time from the splash screen to the main window appearing)
   - loading an entire existing Chandler repository into memory, 1605 items, is
     down to 17s from 32s

Let me know how it works for you !

Andi..