Make releases available under GitHub releases

[octref]

We can provide vsix files so users can easily switch to a pre-built version.
Also a copy of changelog could go there.

[HerringtonDarkholme]

I have released a preview 0.11.8 version and its changelog. https://github.com/vuejs/vetur/releases/tag/0.11.8

@octref we still need publish it via vsce. Do you have time to give it a look?

[DrSensor]

Hello, is it possible/good-idea to make the release cycle of Vetur be the same as typescript/vscode? (using ci like greenkeeper or bot for checking vscode/typescript release then doing auto pr)

vscode now ships ts 2.8.3

[octref]

I did that for 0.11.8. We'll continue to do it for each releases.
I think what we want is continuous release only for VLS (not for Vetur extension). I opened #786 for that.