[Ogdl-core] Spec change (in level 2)

[Rolf V. <rol...@gm...>]

Hi, all. I was never happy with the level 2 grammar (the part that
allows cycles).
It was two complex from my point of view, and difficult to implement.
I've updated
the spec with a small change in that section, so that only one syntax for cycles
remains:

a
  b
c
  #{2

Here, 'c' links to the node 2 lines above. Since in the canonical form of OGDL
there are not more than one node on each line, the number is a coordinate in
the vertical direction and identifies uniquely a node. Negative numbers point
to nodes after the current node.

Kind regards
Rolf.