my_plot_func: Multiple lines in a figure

function [] = my_plot_func(fig_file, topre_file, out_file, varargin)
% varargin:
%     any number of filenames of output files.
%     These output files will be all plotted on the same figure.
%     eg.
%         my_plot_func('myfig', 'mypredict', 'myout', 'myout.track',
'myout.smooth')
%     then there will be 4 lines on the figure, including groundtruth
and 3 outputs.
Merge pull request #4 from WeiTang114/plot_multiple_a_time

my_plot_func: Multiple lines in a figure