publish docs on GH pages

ci/after-success.sh

@@ -0,0 +1,20 @@
+set -euxo pipefail
+
+main() {
+    cargo doc
+
+    mkdir ghp-import
+
+    curl -Ls https://github.com/davisp/ghp-import/archive/master.tar.gz |
+        tar --strip-components 1 -C ghp-import -xz
+
+    ./ghp-import/ghp_import.py target/doc
+
+    set +x
+    git push -fq https://$GH_TOKEN@github.com/$TRAVIS_REPO_SLUG.git gh-pages && echo OK
+}
+
+# only publish on successful merges to master
+if [ $TRAVIS_BRANCH = master ] && [ $TRAVIS_PULL_REQUEST = false ] && [ $TARGET = x86_64-unknown-linux-gnu ]; then
+    main
+fi