Set up Hugo release flow on CircleCI

This rewrites the release logic to use CircleCI 2.0 and its approve workflow in combination with the state of the release notes to determine what to do next.

Fixes #3779

.circleci/config.yml

@@ -0,0 +1,49 @@
+defaults: &defaults
+  working_directory: /go/src/github.com/gohugoio
+  docker:
+      - image: bepsays/ci-goreleaser:0.30.5-2
+    
+version: 2
+jobs:
+  build:
+    <<: *defaults
+    steps:
+      - checkout:
+          path: hugo
+      - run:
+            command: |
+                git clone git@github.com:gohugoio/hugoDocs.git
+                cd hugo
+                make vendor
+                make check
+      - persist_to_workspace:
+          root: .
+          paths: .
+  release:
+    <<: *defaults
+    steps:
+      - attach_workspace:
+          at: /go/src/github.com/gohugoio
+      - run:
+            command: |
+                    cd hugo
+                    git config --global user.email "bjorn.erik.pedersen+hugoreleaser@gmail.com"
+                    git config --global user.name "hugoreleaser"
+                    go run -tags release main.go release -r ${CIRCLE_BRANCH}
+
+workflows:
+  version: 2
+  release:
+      jobs:  
+        - build:
+            filters:
+              branches:
+                only: /release-.*/
+        - hold:
+            type: approval
+            requires:
+              - build
+        - release:
+            context: org-global
+            requires:
+              - hold