[WIP] Create CircleCI config (#484)

* [ci] Create CircleCI config
* Fix typos in container versions
* Add CircleCI badge

.circleci/config.yml

@@ -0,0 +1,63 @@
+version: 2.0
+
+jobs:
+  # Base test configuration for Go library tests Each distinct version should
+  # inherit this base, and override (at least) the container image used.
+  "test": &test
+    docker:
+      - image: circleci/golang:latest
+    working_directory: /go/src/github.com/gorilla/mux
+    steps: &steps
+      - checkout
+      - run: go version
+      - run: go get -t -v ./...
+      - run: diff -u <(echo -n) <(gofmt -d .)
+      - run: if [[ "$LATEST" = true ]]; then go vet -v .; fi
+      - run: go test -v -race ./...
+
+  "latest":
+    <<: *test
+    environment:
+      LATEST: true
+
+  "1.12":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.12
+
+  "1.11":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.11
+
+  "1.10":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.10
+
+  "1.9":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.9
+
+  "1.8":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.8
+
+  "1.7":
+    <<: *test
+    docker:
+      - image: circleci/golang:1.7
+
+workflows:
+  version: 2
+  build:
+    jobs:
+      - "latest"
+      - "1.12"
+      - "1.11"
+      - "1.10"
+      - "1.9"
+      - "1.8"
+      - "1.7"

README.md

@@ -2,6 +2,7 @@
 
 [![GoDoc](https://godoc.org/github.com/gorilla/mux?status.svg)](https://godoc.org/github.com/gorilla/mux)
 [![Build Status](https://travis-ci.org/gorilla/mux.svg?branch=master)](https://travis-ci.org/gorilla/mux)
+[![CircleCI](https://circleci.com/gh/gorilla/mux.svg?style=svg)](https://circleci.com/gh/gorilla/mux)
 [![Sourcegraph](https://sourcegraph.com/github.com/gorilla/mux/-/badge.svg)](https://sourcegraph.com/github.com/gorilla/mux?badge)
 
 ![Gorilla Logo](http://www.gorillatoolkit.org/static/images/gorilla-icon-64.png)