rileyjmurray/sageopt: automatic dualization, options for ordinary sage, bugfixes.

Usually, I'm inclined to only create "releases" for major or minor updates (x.y.0). This release (0.5.3) is created for integration with Zendo, so sageopt can be assigned a DOI for future citation purposes.

There are a few new low-level features in PrimalSageCone and DualSageCone objects. The features affect how these abstract constraints are compiled into standard forms, and subsequently passed to a solver. The functionality exposed by the new features enables solving some problems which previously had numerical issues. Refer to the changelog for information on these.