Automatic Timeseries Ticks

Hi @masayuki0812,
fine work you have done with this project, i like it a lot ;-)

I needed the timeseries to make its ticks automaticlly, so i made a switch.
If you set axis.x.ticks.automatic=true on a timeseries the ticks will be set automatically 
this is helpfull when brushing.

I hope you like it. 

Maybe you have a better idea for the naming, are there conventions? 

I would like to help you with c3 in general let me know if can do anything.

Best wishes,

Thomas