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__
TST: Test invlogit stability.
ENH: More numerically stable version of invlogit.
STY: Pep-8
ENH: More numerically stable inv. nbinom.
STY: Pep-8
REF/ENH: Use clip pattern. Use it for resid_dev in Poisson.
DOC: Fix versions to match other docs.
Merge pull request #2029 from jseabold/update-versions

DOC: Fix versions to match other docs.
Merge pull request #2028 from jseabold/invlogit-stable

ENH: Fix numerical issues in links and families.
DOC: Silence fit.
ENH: Allow user to control formula namespace depth.
DOC: Add eval_env to documentation.
DOC: Add eval_env note to release notes.
DOC: What it is what it is.