new function Progress
use different API
Merge branch 'master' into progress
revert to Write-Output for now
add verbose progress messages
Merge pull request #15 from krlmlr/progress

nicely formatted progress messages, but no color yet
Merge branch 'master' into 5-artifacts

Conflicts:
	scripts/appveyor-tool.ps1
q-n-d hack for forward-backward-slash confusion