Build API documentation with cargo doc.

Makefile

@@ -183,3 +183,6 @@ publish-release:
 # must install graphviz for `dot`
 dep-graph:
 	cargo deps --optional-deps --filter wasmer-wasi wasmer-wasi-tests wasmer-kernel-loader wasmer-dev-utils wasmer-llvm-backend wasmer-emscripten wasmer-emscripten-tests wasmer-runtime-core wasmer-runtime wasmer-middleware-common wasmer-middleware-common-tests wasmer-singlepass-backend wasmer-clif-backend wasmer --manifest-path Cargo.toml | dot -Tpng > wasmer_depgraph.png
+
+docs:
+	cargo doc --features=backend-singlepass,backend-llvm,wasi,managed

azure-pipelines.yml

@@ -211,6 +211,24 @@ jobs:
           tag: dev
           assets: $(Build.ArtifactStagingDirectory)
 
+  - job: Docs
+    pool:
+      vmImage: "ubuntu-16.04"
+    variables:
+      rust_toolchain: nightly-2019-08-15
+    steps:
+      - checkout: self
+        submodules: true
+      - template: .azure/install-rust.yml
+      - template: .azure/install-llvm.yml
+      - template: .azure/install-sccache.yml
+      - template: .azure/install-cmake.yml
+      - bash: |
+          make docs
+        displayName: Build documentation
+    variables:
+      rust_toolchain: stable
+
 # We only run the pipelines on PRs to Master
 pr:
   - master