nightly-2021-06-02

Changes since nightly-2021-06-01:

Full commit log

• 7839f2c doc: direct link & instructions for elan on Windows
• 812c8d0 doc: clarify Windows limitations
• 3499016 chore: improve error message when compiling code containing axioms or noncomputable definitions
• 3fb7a2c fix: make problematic Ord -> LT instance a def
• fb9c191 feat: prototype for equality theorem generator for auxiliary match functions
• 764ccc4 chore: add default value for parameter
• 7303761 feat: add modifyTarget
• 97ac231 feat: add missing OptionT instance
• 4062dee fix: fixes #498