[yt-dev] [yt_analysis/yt] Standardize arguments to plot annotations (issue #547)

[Matthew Turk]

New issue 547: Standardize arguments to plot annotations
https://bitbucket.org/yt_analysis/yt/issue/547/standardize-arguments-to-plot-annotations

Matthew Turk:

`plot_args` and `text_args` should only be one or the other.  Having multiple argument names is confusing.

Responsible: MatthewTurk