Enable Appveyor CI once again

Appveyor just moved their build environment. Perhaps they are running on
more modern hardware now. Let's try again.

Author: ruuda

.appveyor.yml

@@ -0,0 +1,23 @@
+environment:
+  matrix:
+    - target: nightly-x86_64-pc-windows-msvc
+
+install:
+  # Download the Rust and Cargo installer.
+  - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-${env:target}.msi"
+
+  # Install Rust and Cargo and wait for installation to finish by using Write-Output.
+  - ps: msiexec /package "rust-${env:target}.msi" /quiet /norestart | Write-Output
+
+  # Pick up the new Path variable after the installer modified it.
+  - ps: $env:Path = [System.Environment]::GetEnvironmentVariable("Path","Machine")
+
+  # Print versions for future reference.
+  - rustc --version
+  - cargo --version
+
+build_script:
+  - cargo build
+
+test_script:
+  - cargo test

readme.md

@@ -67,3 +67,5 @@ Convector is free software. It is licensed under the
 [gplv3]:        https://www.gnu.org/licenses/gpl-3.0.html
 [interactive]:  https://raw.githubusercontent.com/ruuda/convector/master/screenshots/interactive.png
 [accumulative]: https://raw.githubusercontent.com/ruuda/convector/master/screenshots/accumulative.png
+[ci-img]:       https://ci.appveyor.com/api/projects/status/468h0bilnnrsrnyy?svg=true
+[ci]:           https://ci.appveyor.com/project/ruuda/convector