ci: add appveyor build (windows)

Author: sbinet

appveyor.yml

@@ -0,0 +1,19 @@
+build: off
+
+clone_folder: c:\gopath\src\github.com\go-python\gpython
+
+branches:
+  only:
+    - master
+
+environment:
+  GOPATH: c:\gopath
+  PATH: '%GOPATH%\bin;%PATH%'
+
+stack: go 1.10
+
+build_script:
+  - go get -v -t -race ./...
+
+test_script:
+  - go test -race ./...