Progress
========

The progress and final grade of a student must be calculated from the grades of 3 exams.

    #. The progress is a string with the following possible values:
    
        - ``constant`` if all grades are equal.
        - ``positive`` if every grade is greater or equal than the previous one (and is not constant).
        - ``negative`` if every grade is less or equan than the previous one (and is not constant).
        - ``peak`` if the second grade is greater than the other two.
        - ``valley`` if second grade is less than the other two.
                
    #. The average is calculated as the average of the **two best** partial grades (the worst is **discarded**) except if the progress is ``negative`` where no grade will be discarded. 
    
If any of the 3 given grades is not between 0.0 and 10.0 included, then will consider that an error happened. In this case, no matter what, the progress must be ``error`` and the average -1.0.

Please, implement the following Python function in the module :mod:`progress` (file :file:`progress.py`) according to the following specification:

    ``progress(g1, g2, g3)``
        | *takes*
        | ``g1, g2, g3`` :class:`float` values
        | *returns* 2 values:
        | - a :class:`str` corresponding to the grades progress as specified above
        | - a :class:`float` corresponding to grades average as specified above and rounded to 1 decimal.

Exemples:
    
    .. literalinclude:: progress-test.txt
      :language: python3
      :lines: 3-
    
Doctests are available at the :download:`progress-test.txt` file.