Feature request: plot fraction of reads on the y-axis and choose bin size for error plotting

Hi,
It would be great to be able to view the error plots normalised by the total reads in the bin. In addition for long reads it would be useful to set a constant bin size, as the default size of 1 --> 10 --> 50 --> 100 is too small at first (and even 100 might be slightly small when mean read length is 10Kbp).
Great and easy to use though.
Cheers.