add appveyor ci

.appveyor.yml

@@ -0,0 +1,15 @@
+environment:
+  matrix:
+  - TARGET: x86_64-pc-windows-msvc
+  - TARGET: i686-pc-windows-msvc
+  - TARGET: x86_64-pc-windows-gnu
+  - TARGET: i686-pc-windows-gnu
+install:
+  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-nightly-${env:TARGET}.exe" -FileName "rust-nightly.exe"
+  - ps: .\rust-nightly.exe /VERYSILENT /NORESTART /DIR="C:\rust" | Out-Null
+  - ps: $env:PATH="$env:PATH;C:\rust\bin"
+  - rustc -vV
+  - cargo -vV
+build: false
+test_script:
+  - cargo test --verbose