update to version v0.6.0
* use version-specific travis environments
* tox/travis: enable tests on py3.5
* add a comment: this check doesn't catch non-None returns
* improve function-is-empty test to work on py3.6 too
* add more metadata to setup
* graphviz() -> asDigraph()
* Use inspect.getfullargspec on Py3 to avoid deprecation warnings with inspect.getargspec
* add tracing API, with docs
* Conform author metadata to `distutils.core` API
* tracer can return a callable to see Output invocations
* Make hashable classes frozen for attrs 17.1.0 (fixes #62).
* Assert that 'input' function bodies are empty, to avoid surprises.
* reject duplicate transitions (same starting state and input)
* tox/travis: enable tests on py3.6
* improve tests: more cases, make pyflakes-clean
* sigh, add more code to attain full test coverage
* make setTrace a private API, document cautions about its use
* cover the specimen functions in tests, remove ordify()
* cleanup: s/assert_no_code/assertNoCode/
- convert to singlespec
- fix Source url