0.3.1

Added

• Added Binder setup description and links from documentation.
• Added test framework with pytest and set up first batch of tests.
• Added Python 3.7 configurations to CI configurations.

Changed

• Updated pybind11 to v2.2.3.
• Updated documentation, changing examples from simple reStructuredText to Jupyter notebooks, executable through Binder.

Fixed

• Fixed parselmouth.praat.run_file to include files from directory of the script file, but to run in the original working directory.
• Corrected typo in Sound.to_harmonicity_ac and to_harmonicity_cc (see #6).