github actions: build windows repl exe

.github/workflows/repl.yml

@@ -0,0 +1,32 @@
+# Manually triggered action to build a Windows repl.exe which users can
+# download to debug complex bugs.
+
+name: Build Windows REPL .exe
+
+on:
+  workflow_dispatch:
+
+jobs:
+  build_repl:
+    name: Build REPL example
+    runs-on: windows-latest
+    steps:
+    - uses: actions/checkout@master
+
+    - name: Install Rust
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: 1.50.0
+        override: true
+
+    - name: build
+      uses: actions-rs/cargo@v1
+      with:
+        command: build
+        args: --example repl --features repl,vendored
+
+    - name: Upload binary
+      uses: actions/upload-artifact@v2
+      with:
+        name: repl.exe
+        path: 'target/debug/examples/repl.exe'