[MRG+1] PR for model_evaluation.rst changes to fix issue #3661, "Document negation of loss as scoring parameter"

* doc/modules/model_evaluation.rst in the MattpSoftware fork contains my changes for issue #3661.

* issue-3661/model_evaluation_copy_edited.rst also fixes typos I found when reading the document.

* issue-3661/model_evaluation_edit_notes.txt has the explanation for the changes in model_evaluation_copy_edited.rst, and flags a few other other items for questions.
Would you agree to replacing the statement with two changes:

1. Adding a comment before creating the log_loss classifier:
    >>> # using log_loss requires enabling probability estimates
    >>> clf = svm.SVC(probability=True,random_state=0)
    >>> cross_validation.cross_val_score(clf, X, y, scoring='log_loss') #
doctest: +ELLIPSIS

2. Modifying the note to mention that the function list is generated by
setting the scoring parameter to the wrong value, and adjusting some of the
other verbiage

.. note::

    The ValueError exception above is caused by setting the ``scoring``
    parameter to an unknown value. The exception message lists all the
    acceptable values, corresponding to the functions measuring
    prediction accuracy described in the following sections.
    The scorer objects for these functions are stored in the dictionary
    ``sklearn.metrics.SCORERS``.


On Wed, Oct 1, 2014 at 4:24 PM, jnothman <notifications@github.com> wrote:

> In doc/modules/model_evaluation.rst:
>
> >  Setting the ``scoring`` parameter to a wrong value should give you a list
> > -of acceptable values::
> > +of acceptable values.  To use :func:`log_loss` as the scorer, enable
>
> Please move this statement on enabling probability estimates to a separate
> paragraph below the .. note::.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/scikit-learn/scikit-learn/pull/3706/files#r18314884>.
>