py-dot: updated to 1.4.2

1.4.2

Added:
- Documentation: Basic usage examples in `README.md`.

Changed:
- More detailed error message in case of Graphviz errors.
- More detailed warning message in case of failure to import the DOT
  parser module.

Deprecated:
- A future pydot 2.0.0 will drop support for Python 2, 3.4 and
  possibly other Python versions that are end-of-life at that time.
  Pydot does not emit any deprecation warnings about this. Further
  pydot 1.x.x releases are currently not foreseen, but if there are
  any, should still support the mentioned Python versions.

Fixed:
- On Python 2, non-equality comparison (`!=`) between two separate, but
  equal `Edge` instances will now correctly return `False`, as it
  already did on Python 3.
- Prevent `TypeError` in handling of DOT parser error.
- Prevent `TypeError` in `graph_from_adjacency_matrix()` and
  `graph_from_incidence_matrix()`.
- Prevent `TypeError` when creating an edge with a `Subgraph` or
  `Cluster` object (as opposed to name string) as an edge point.
- Windows only: Fixed most failures to find Graphviz when a conda or
  Anaconda installation exists, but Graphviz was installed manually or
  through pip (`.bat`/`.exe` suffix problem).
- Windows only: Fixed failure to run Graphviz related to side-by-side
  assembly (SxS) by now propagating the `SYSTEMROOT` environment
  variable.


(adam)