The function plots x and y data with errorbars for both.
x=array of xdata
y=array of ydata
xerror=array of errors for x
yerror=array of errors for y
s=string argument for plotting the datapoints, The errorbars are plotted in red and blue
Needs a figure to plot in.
errorbars are symmetrical, that means that the function plots [x-xerror x+xerror] and [y-yerror y+yerror].
x,y,xerror,yerror must all be arrays.