[Gzz] Lately (Benja)

[B. Fallenstein]

What I've mostly been doing:
- Work on saving

(Note: I've added a new core interface, Slicer, moved a second interface 
to core, SliceVersion, and made slight changes to others; see my commit 
message.)

Things I've also done:
- Read about URI schemes
- Think about vobs; mediaserver uris; ids for single characters; 
implicit looping (as in, "excise all marked cells on all dimensions") 
for the zaubertrank (read about Icon for that)
- Wondered whether I have any basis for considering zzstructure "better" 
than labelled graphs a la RDF (in some ways zz is more confining; in 
some ways labelled graphs are more confining; I think labelled graphs 
may be easier to understand)