Implementation of original Circos style ticks label plot function

[moshi4]

Hi,

Thank you for developing a very nice Circos plotting tool implemented in Python.

pyCircos currently implements a tickplot function to plot ticks on a Garcs object, but it does not support tick label plotting in the original Circos style as shown below.

Since tick plots like the one shown above are often used, I think pyCircos would be better off if this function is implemented.