Build Rust extension in CI.

Author: thedrow

.travis.yml

@@ -57,7 +57,7 @@ before_install:
 
 install:
   - pip --disable-pip-version-check install -U pip setuptools wheel | cat
-  - pip --disable-pip-version-check install -U tox | cat
+  - pip --disable-pip-version-check install -U tox pyo3-pack tox-pyo3 | cat
 script: tox -v -- -v
 after_success:
   - .tox/$TRAVIS_PYTHON_VERSION/bin/coverage xml