Adding upstream version 1.2.3.

Signed-off-by: Daniel Baumann <daniel@debian.org>

.appveyor.yml

@@ -0,0 +1,29 @@
+version: "{build}"
+clone_depth: 1
+clone_folder: c:\outside-gopath
+environment:
+    GOPATH: c:\gopath
+    GO111MODULE: on
+install:
+    - echo %PATH%
+    - echo %GOPATH%
+    - go version
+    - go env
+    - go get -v -t -d ./...
+build: off
+test_script:
+    - go build ./selfupdate
+    - go build ./cmd/selfupdate-example
+    - go build ./cmd/detect-latest-release
+    - go build ./cmd/go-get-release/
+    - ps: |
+        if (Test-Path env:GITHUB_TOKEN) {
+            go test -v -race "-coverprofile=coverage.txt" ./selfupdate
+        } else {
+            go test -v -race -short ./selfupdate
+        }
+after_test:
+    - "SET PATH=C:\\Python34;C:\\Python34\\Scripts;%PATH%"
+    - pip install codecov
+    - codecov -f "coverage.txt"
+deploy: off