Confusion over ltr.train and ltr.ranklib

[binarymax]

We have different modules that seemingly do the same thing and it's causing confusion. See the Netfix movies notebooks, lots of references to from ltr import train but there is no module train. There IS a module ltr.ranklib. We need to figure out and clean up the module dependencies.

[nathancday]

Consolidate this to one function with named params/args for exposing anything that ranklib can take.

As bigger picture we should probably have inherited args from train thru kcv and featureSearch.