Release v2.3.1

Added

• cratis screenplay generate produces a Cratis Screenplay .play document from the source of an Arc application, without running it (#44)
• cratis screenplay validate compiles .play files and reports their diagnostics, exiting non-zero when any are errors

Fixed

• Projects whose resource classes are generated during the build are read correctly, instead of appearing not to compile (#49)
• The generated document is written even when generation reports errors, so a partial result can be inspected rather than lost (#49)