reject circular dependencies within tasks and workflows (chanzuckerbe…

…rg#90)

closes chanzuckerberg#43

miniwdl cromwell MVP (chanzuckerberg#75)

miniwidl cromwell provides a nicer command-line interface for running a workflow locally using Cromwell.

Update README.md

CLI: indicate non-called tasks only when there is a top-level workflow

called workflows must declare their outputs + doc improvements

Update README.md

Refine linters

setuptools and pbr packaging for PyPI (chanzuckerberg#25)