ci: generate docs (#1810)

Check docs as part of CI. This should catch link errors.

ci/azure-check-docs.yml

@@ -0,0 +1,15 @@
+jobs:
+# Check docs
+- job: ${{ parameters.name }}
+  displayName: Check docs
+  pool:
+    vmImage: ubuntu-16.04
+  steps:
+    - template: azure-install-rust.yml
+      parameters:
+        rust_version: ${{ parameters.rust }}
+
+    - script: |
+        RUSTDOCFLAGS="--cfg docsrs" cargo doc --lib --no-deps --all-features
+      displayName: Check docs
+

ci/azure-test-stable.yml

@@ -17,7 +17,6 @@ jobs:
   steps:
   - template: azure-install-rust.yml
     parameters:
-      # rust_version: stable
       rust_version: ${{ parameters.rust }}
 
   - script: cargo install cargo-hack