appveyor restore github release

update appveyor, remove github deployment for now, bump version to 2.9.1

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)