ENH: add a choice of methods for ranking ties in stats.rankdata
ENH: add the 'ordinal' method to stats.rankdata.
ENH: Improve the performance of the 'ordinal' method of stats.rankdata.
DOC: small fix to the docstring of stats.rankdata
Merge pull request #447 from WarrenWeckesser/rankmethods

ENH: add a choice of methods for ranking ties in stats.rankdata