ENH/REF: Accept style args; use plot, not scatter.

Now `annotate` uses `plot`, which is both faster and more flexible than `scatter` in this context. It accepts dictionaries in `plot_style` and `imshow_style` which override hard-coded defaults.

There is some funny-business with `extent` aimed at getting this:

![image](https://cloud.githubusercontent.com/assets/2279598/4241341/f35c70c8-39f2-11e4-8f98-198288c303c6.png)

not this:

![image](https://cloud.githubusercontent.com/assets/2279598/4241426/c8742fb2-39f3-11e4-8a31-fffedba9f3b8.png)

@tacaswell if you know a better way, have at it!
Good catch. Updated.

On Fri, Sep 12, 2014 at 10:40 AM, Thomas A Caswell <notifications@github.com
> wrote:

> In trackpy/plots.py:
>
> >                    vmin=kwargs.get('vmin'), vmax=kwargs.get('vmax'))
> > -        ax.set_xlim(0, superimpose.shape[1]*mpp)
> > -        ax.set_ylim(0, superimpose.shape[0]*mpp)
> > +        ax.set_xlim(-0.5, (superimpose.shape[1] - 0.5) * mpp)
>
> you need the mpp on the lower limit as well
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/soft-matter/trackpy/pull/155/files#r17482005>.
>