[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.
Modify the parameter description to use your verbiage about models?

* whether the python function returns a score (``greater_is_better=True``,
  the default) or a loss (``greater_is_better=False``).  If a loss, the
output
  of the python function is negated by the scorer object, conforming to
  the cross validation convention that scorers return higher values for
better models.


On Wed, Oct 1, 2014 at 4:27 PM, jnothman <notifications@github.com> wrote:

> In doc/modules/model_evaluation.rst:
>
> >
> >  - functions ending with ``_error`` or ``_loss`` return a
> > -  value to minimize (the lower the better).
> > +  value to minimize, the lower the better.  When converting
> > +  into a scorer object using :func:`make_scorer`, set
> > +  the ``greater_is_better`` parameter to False (True by default).
>
> Now that I see you mention it below, I'm not sure it needs to be here, but
> do refer here to the custom scorer object discussion below.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/scikit-learn/scikit-learn/pull/3706/files#r18315003>.
>