Log Message:
0.15

Features:

* Issue 39: Traceback with for a syntax error when compiling async function

  On Python 3.5 some (invalid) async function definitions caused a modulegraph
  traceback, instead of adding "InvalidSourceModule" nodes to the graph.

* Issue 40: The graph now contains nodes of type \ 
"InvalidRelativeImport" for
  attempts to use relative imports that walk outside of a toplevel
  package.

Bugfixes:
* Issue 38: Dot output broken in Python 3
* Issue 36: Make sure test suite works on systems other than macOS
* Add support for "async def" to the AST scanner, needed to
  properly recognize imports in async function definitions.