DOC: merge wiki edits for ndimage.filters by hand.

These functions use misc.docfiller, so shouldn't have been edited in the wiki.
I marked all these functions as unimportant there now.
DOC: merge wiki edits, cluster, constants and fftpack modules.
DOC: merge wiki edits, interpolate module.
DOC: merge wiki edits, lib, io, misc modules and main docstring.
DOC: merge wiki edits, linalg module.
DOC: merge wiki edits, ndimage module.
DOC: merge wiki edits, optimize module.
DOC: merge wiki edits, signal module.
DOC: merge wiki edits, spatial module.
DOC: merge wiki edits, stats module.
DOC: merge wiki edits, sparse module.
MAINT: address review comments of Josef.
DOC: address review comments on PR-405 from Warren.
Merge branch 'merge-wiki-edits' into master

Reviewed at https://github.com/scipy/scipy/pull/405

Conflicts:
	scipy/interpolate/interpolate.py
	scipy/interpolate/polyint.py
	scipy/signal/signaltools.py
	scipy/stats/morestats.py
	scipy/stats/stats.py