myplot: conveniently plotting multiple curves in 2D

A wrapper of "plot'. Multiple calls of myplot generate curves automatically cycling through a sequence of styles and colors.

% A wrapper of "plot" for convienient 2D-plot of multiple curves.
% Multiple calls of myplot (with 'hold' switched on) generate curves
% automatically cycling through a sequence of styles and colors,
% and automatically numbered in the legend.
% By Chi-Hang Lam, Jan 2019
%
% Usage: myplot( [<options>], [<arguments>], ... )
% <arguments> :
% arguments to be sent to the 'plot' function
% <options>:
% 'll' 'lx' 'ly' :set log-log or semi-log scales
% 'po' 'li' 'lp' :set style of this and subsequent curves to point, line, or linepoint
% 'dot' 'dash' 'dashdot' :set line style to dotted, dashed, or dashed-dotted
% 'style', <style> :set default style to <style> = 'po', 'li', or 'lp'
% 'color',<index> :set color based on <index>
% 'marker',<index> :set marker based on <index>
% 'noinc' :do not automatically advance to next color/marker for this curve
% 'group', <n> :sebsequent cuvers advance to next marker/color after every <n> curves
% 'ctitle',<ctitle> :set curve label to <ctitle> in legend
% 'noleg' :do not show curve in legend
% 'clear' :clear plot and reset curve counter
% 'graph',0 :do not plot this curve, i.e. neglect this function call
% 'jet',<ncolor> :use matlab's jet colormap with <ncolor> colors for this curve
%
% Arguments and options can be mixed in arbitrary order
% Requires: getopt.m
% e.g. x=1:10; hold on; myplot('ll', x,x); myplot(x,2*x);
% See myplotdemo.m for more examples