about new plotting options



A few comments about new plotting options.

 * rem_plot_option: let's spell out "remove".

 * gnuplot_prefix / gnuplot_preamble: I gather that these two are the
   same. I'm implacably opposed to aliases, as they are nothing but a
   source of trouble. Let's nuke one or the other, I don't care which.

 * samexy, samexyz, yxratio, maybe others: can we write these with an
   underscore to separate distinct semantic bits, e.g., same_xy,
   same_xyz, yx_ratio. Especially for speakers of languages other than
   English, it is hard to see where to break the semantic units (but
   it's hard enough for native speakers too).

FWIW

Robert Dodier