Pydotz

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- Nothing changed yet.

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- Make graph, edge, node attributes order deterministic
- Fix string formatting after catching error (201)

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- Installation of pydot in conda env on Windows directly supported
- Fixed comparing of SHA hash in regression tests (which fail now)

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- Dropped Python 2.6 support (185)
- Move errno from os to builtin. Fixes 177 (191, 182)

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- ENH: propagate `LD_LIBRARY_PATH` when calling GraphViz
- API: raise `OSError` when a GraphViz executable is not found
- API: add method `__str__` to classes `Node, Edge, Graph`
- API: add arg `encoding` to `Dot` methods `create, write`
- API: quote cluster names when necessary
- API: give source and destination nodes as separate args to `Edge.__init__`
- API: never ignore `src, dst`, overwrite if `points` defined in `obj_dict`

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- support Python 2.6
- several corrections
- quote empty strings to avoid graphviz errors