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.
Added function to determine Nyquist plot

Code based on the lti.bode() function.
n=10000 decided through trial and error. Might be somewhat high for
simple systems.
improved nyquist() function

added testing and changed return values as suggested by rgommers and
ewmoore
DOC: Add BSD rationale to FAQ
changed name to freqresp()

Changed the name as suggested on the Mailing List and adjusted the
docstrings
BUG: special/cdflib: sharper absolute tolerances in distribution fcn tails (#955)
MAINT: update gitattributes
BUG: special: fix mathieu* return values in undefined cases
TST: special: dump data for Mathieu from GSL, and test against it