4.2a4

Yet another pre-release to support rendering pretty graphs in roboticsbook.org

Major changes:

• a pretty big big-fix: DiscreteFactorGraph::optimize now does MPE! #1050
• @dellaert also changed API (breaking!) of Subgraph Preconditioners to include fewer shared_ptrs. #1010
• @lucacarlone landed robust triangulation, great for GTSFM as well!

New Contributors

• @magicbycalvin made their first contribution in #1042
• @senselessDev made their first contribution in #1059

What's Changed since 4.2a3

• Robust triangulation by @lucacarlone in #1020
• DiscreteBayesNet sample/optimize variants by @dellaert in #1043
• Added a convenience function for plotting 2D points. by @magicbycalvin in #1042
• Some discrete improvements by @dellaert in #1045
• Subgraph API change by @dellaert in #1010
• Update python install in CI by @varunagrawal in #1054
• Fix DiscreteFactorGraph::optimize to return MPE by @dellaert in #1050
• Changes in gtsam to support hybrid branches by @dellaert in #1055
• Expose GraphvizFormatting and test in python by @senselessDev in #1059
• Add position to Point2 nodes in GraphViz by @senselessDev in #1058
• Fix docs by @dellaert in #1064
• Added sumProduct as a convenient alias by @dellaert in #1066