Add the readfile function.

- :code:`run`: Runs a command and returns the stdout, stderr and returncode

  using run_. This function replaces the :code:`run` filter.

- :code:`readfile`: Returns the contents of a file.

Example usage can be seen in :code:`tests` and for specific filters in the

docstrings in :code:`template/functions.py`.

        proc["stdout"] = proc["stdout"].decode()

        proc["stderr"] = proc["stderr"].decode()

    return proc

def readfile(path):

    """

    Opens a file, returns the contents.

    >>> readfile("/dev/null")

    ''

    >>> foo = "foo"

    >>> with open("/tmp/foo", "w") as f:

    ...     f.write(foo)

    3

    >>> foo == readfile("/tmp/foo")

    True

    """

    with open(path, "r") as f:  # pylint: disable=invalid-name

        return f.read()