Remove dependency on multiple max drawdown functions

[gusgordon]

Currently, we have max_drawdown and get_max_draw_down, the latter likely being the better version.

[twiecki]

Yes, I noticed that too. We should try to have the plot use only the latter version and remove max_drawdown.

[gusgordon]

These actually do different things, get_max_draw_down just gets the extrema dates. These definitely need renaming, but maybe there is a good way to combine them.

[twiecki]

We can probably call gen_drawdown_table(df_rets, top=1) and get the drawdown value from there https://github.com/quantopian/quantrisk/blob/master/quantrisk/timeseries.py#L368

[eigenfoo]

Couldn't find a get_max_draw_down function in the code base, assuming this issue has been resolved.