replaced \n with \r\n in ReadMe file
Change the plot theme grey to bw

The bw theme is better than the grey theme,
when the plotted graph is pasted to keynote slide
add ylimit set to plot function

plot function now has a arg. of ylimit
TODO:asking user the ylimit is not implemented
Add limit_setter function

limit setter is now available.
Change the saving size of PDF

20*12 is too big to paste the graph to slide and so on,
so change to 12.5*7.5
ratio 5:3 is keeped