CI: Publish Windows binaries

[chfast]

Currently the package of Windows binaries is created in AppVeyor builds and available as a build artifact.
There are 2 options to automate deployment for releases.

• Use AppVeyor deployment scripts as in https://github.com/ethereum-mining/ethminer/blob/master/appveyor.yml#L42-L55.
• Use ghr tool (golang) to deploy packages as in https://github.com/ethereum/aleth/blob/master/circle.yml#L224-L234.

I prefer the second option because traditional CI deployment scripts are quite flaky and with ghr we will use the same script on every CI platform.

cc @gumb0 @halfalicious

[chfast]

Still a quick workaround is to find the mentioned artifact and upload it manually to a GitHub release.

[damian123]

Would love to see an official Windows release, like on Linux and MacOS.
What would be needed for this to happen. Do we need setup CI build and test bots?