Improved doc strings for plotting functions
Improved doc strings for plotting functions

Added a few comments on the axis formatting and tried to
structure things so that they will be slightly less incomprehensible
in two months time.

scikit-optimize/scikit-optimize,betatim/BlackBox,glouppe/scikit-optimize,scikit-optimize/scikit-optimize,glouppe/scikit-optimize,betatim/BlackBox,ccauet/scikit-optimize