DOC: Narrative doc for median_absolute_error
ENH: Reworked _modified_weiszfeld_step
DOC: Improved _spatial_median docs
COSMIT: Replaced xrange by range

range still is xrange:
from sklearn.externals.six import xrange as range
COSMIT: Renamed y -> x_old in _modified_weiszfeld_step
COSMIT: Renamed spmed[_old] to spatial_median[_old]
COSMIT: Break and for .. else in _spatial_median
ENH: Reworked _lstsq in theil_sen.py
ENH: Replace AssertionError by ValueError
COSMIT: Improved error message in theil_sen.py
COSMIT: Renamed n_all to all_combinations in theil_sen.py
COSMIT: Consistent naming for n_subpop
COSMIT: Fixed pep8 problem in theil_sen.py