Add appveyor integration

Author: liufengyun

.appveyor.yml

@@ -0,0 +1,21 @@
+version: '{build}'
+os: Windows Server 2012
+install:
+  - cmd: choco install sbt -ia "INSTALLDIR=""C:\sbt"""
+  - cmd: SET PATH=C:\sbt\bin;%JAVA_HOME%\bin;%PATH%
+  - cmd: SET SBT_OPTS=-XX:MaxPermSize=2g -Xmx4g
+clone_script:
+  - git clone --depth 50 https://github.com/lampepfl/dotty.git
+  - cd dotty
+  - git submodule update --init --recursive --jobs 3
+build_script:
+  - project/scripts/sbt compile
+  - project/scripts/sbt "dotty-bootstrapped/compile"
+test_script:
+  - project/scripts/sbt test
+  - project/scripts/cmdTests
+  - project/scripts/sbt "dotty-bootstrapped/test"
+  - project/scripts/bootstrapCmdTests
+cache:
+  - C:\sbt\
+  - C:\Users\appveyor\.ivy2