Add QLRest, a quicklook generator for restructuredtext.
user
```ruby
class Qlrest < Cask
  url 'https://github.com/downloads/cluther/qlrest/QLRest.qlgenerator.zip'
  homepage 'https://github.com/cluther/qlrest'
  version '2.0'
  sha256 '7800e17fae9afc640791cf94dcd50f50b1ff2d24ceaeb2f484d1e18b7bf10ea7'
  qlplugin 'QLRest.qlgenerator'
end
```
assistant