appveyor restore github release
update appveyor, remove github deployment for now, bump version to 2.9.1
Merge branch 'develop'
Merge branch 'rmunn-feature/getopt-mode' into develop
prepare for release 2.9
Publish Release 2.8.0
regenerate nuget key and reencrypt
Update readme.md
Add Linux as CI in appveyor (commandlineparser#598)