[LRUG] Graphable lib

[Tim Cowlishaw]

Hey there LRUG,

I decided i needed an easy way to set up graph-like relationships  
between ruby objects for a project, so I knocked together this: http://github.com/timcowlishaw/Graphable/tree/master

If anyone would be willing, I'd really appreciate any thoughts about  
anything i could do to improve it, through refactoring, adding  
features, or removing some of the more egregious hacks (there's some  
nasty hackery with instance_variable_set and instance_variable_get  
that allows a parent object to update it's children's relationship to  
itself, without allowing any other objects to tamper with it (in  
theory) - would be especially interested in nicer ways to do this!)

Cheers,

Tim