ENH: add the Edgeworth expansion based on the normal distribution

Given a set of cumulants, construct a matching distribution
as an asymptotic series starting from the normal distribution.
MAINT: make it work with scipy < 0.13
TST: remove an overly optimistic test
MAINT: remove hermite compat wrapper for numpy < 1.6
DOC: add a note to release notes
MAINT: distributions: tweak the __init__
Merge pull request #1325 from ev-br/edgeworth

ENH: add the Edgeworth expansion based on the normal distribution