Add Appveyor

appveyor.toml

@@ -0,0 +1,23 @@
+environment:
+  matrix:
+    - TARGET: x86_64-pc-windows-gnu
+      RUST_VERSION: stable
+    - TARGET: x86_64-pc-windows-gnu
+      RUST_VERSION: nightly
+
+install:
+  - curl -sSf -o rustup-init.exe https://win.rustup.rs/
+  - rustup-init.exe -y --default-host %TARGET% --default-toolchain %RUST_VERSION%
+  - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
+  - rustc -Vv
+  - cargo -V
+
+# Building is done in the test phase, so we disable Appveyor's build phase.
+build: false
+
+cache:
+  - C:\Users\appveyor\.cargo\registry
+  - target
+
+test_script:
+- cargo test