[vtkusers] Graph library update

[David Duke]

For those interested in graphs,  I've just put up a new version of my 
evolving graph library, built on VTK.  Changes include:

- new filters, including:
     + 2D GEM
     + Harel & Koren's higher-dimensional embedding layout
     + selection of reachable nodes.
- better integration of strings, and a "string mapper".
- tidier management of bends in edges
- conversion to/from unstructured grids
- replacement of floats by doubles in the API, reflecting recently 
announced changes to VTK.

The last change may be a problem for a few people with older (pre 4.4?) 
versions of VTK: an earlier version of the library is still available. 
Many thanks to a number of people who have provided comments and fixes, 
in particular Amir Youssefi.

The library is available at

http://www.cs.bath.ac.uk/~djd/graphs.html


David.