Update this as you finish features so that we don't have to go back and try to figure out what's happened since the last release.

4.2b3

• Support for drag-and-drop rewriting of equivalences in the web UI (PropositionalTactics.equivRewriting)
• Differential auxiliaries are now supported in the tactic library and web ui.
• Improved handling of existential quantifiers that bind variables whose primed symbols occur in the scope of the existential.
• Developers: be aware of changes to build configurations -- names of JAR files are now version-agnostic: keymaerax-core.jar and keymaerax-web.jar.
• Various bug fixes