ENH: improve stats.nanmedian more by assuming nans are rare

Move nans to end of array instead of creating a new array without them.
This is faster under the reasonable assumption that nans are rare.
ENH: add runtime warning for all nan slice of nanmedian
ENH: change to use array view in signal/_peak_finding.py
Merge pull request #3396 from juliantaylor/nanmedian-improve2

ENH: improve stats.nanmedian more by assuming nans are rare
Merge pull request #3273 from pv/pep8

Add PEP8 check to Travis-CI
BUG: modified ClusterNode.pre_order() for non-root nodes.

Fixes gh-2177 by replacing the boolean vectors with sets.
TST: add test for subtree pre_order in cluster.hierarchy.

Tests that ``pre_order`` method works for subtree of ClusterNode root.
MAINT: minor PEP8, test docstring cleanup for previous test_hierarchy commit.
Merge branch 'pr/3394' into master.  Closes gh-2177.

See https://github.com/scipy/scipy/pull/3394
BUG: Center odd size window around index, fixes existing off-by-one eror
MAINT: remove unused function scipy.stats.mstats_basic._kolmog1
MAINT: Fix PEP 8 violation in _peak_finding.py
Merge pull request #3450 from argriffing/remove-kolmog1

MAINT: remove unused function scipy.stats.mstats_basic._kolmog1
Merge pull request #3409 from yotam/master

ENH: change to use array view in signal/_peak_finding.py
ENH: sparse/sparsetools: replace SWIG by manual wrappers
BLD: sparse: update sparsetools build
MAINT: update gitignore re sparsetools
ENH: sparse: split sparsetools to smaller compilation units
ENH: sparse/sparsetools: better autogenerated code + comment the code better
MAINT: sparsetools: delete unused files