Provide README.md converted to reStructuredText format.

def get_long_description():
    """Provide README.md converted to reStructuredText format."""
    try:
        with open('README.md', 'r') as f:
            description = f.read()
    except OSError as e:
        if e.errno != errno.ENOENT:
            raise
        return None

    try:
        process = subprocess.Popen([
                'pandoc',
                '-f', 'markdown_github',
                '-t', 'rst',
            ],
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            universal_newlines=True,
            )
    except OSError as e:
        if e.errno == errno.ENOENT:
            return None
        raise

    description, __ = process.communicate(input=description)
    if process.poll() is None:
        process.kill()
        raise Exception("pandoc did not terminate")
    if process.poll():
        raise Exception("pandoc terminated abnormally")

    return description