BUG: interpolate/fitpack: arguments to fortran routines may not be aliased

Fixes gh-2911
STY: interpolate: deobfuscate fitpack_insert a bit
DOC: simplify examples with semilogx
Merge pull request #3735 from endolith/patch-6

DOC: signal: add minimal docstrings to lti.impulse/step
Merge pull request #3734 from endolith/patch-5

DOC: signal: simplify doc examples with semilogx
Merge pull request #3673 from pv/fitpack-alias-fix

BUG: interpolate/fitpack: arguments to fortran routines may not be aliased
BUG: cast pchip arguments to floats
Merge pull request #3736 from ev-br/pchip_cast

BUG: interpolate: cast pchip arguments to floats

pchip interpolator goes nuts when given integer input. This PR makes sure the arguments are cast to floats.
BUG: special: ellip(k,e)inc nan and double expected value

Both ellipkinc and ellipeinc returned nan for a particular value
due to cancelation in a tangent update formula.  Double the
expected value was returned in a small region around the value
returning nan due to using a fragile argument reduction formula.

Fixes gh-3550
Merge pull request #3704 from ewmoore/ellik_fix

BUG: special: ellip(k,e)inc nan and double expected value
Enable automated testing with Python 3.4
Merge pull request #3750 from frewsxcv/patch-1

Enable automated testing with Python 3.4
ENH: add multivariate normal option to return the effective rank
MAINT: remove return_rank optional argument, add .rank multivariate_normal_frozen attribute, add tests
MAINT: learn how to use frozen distributions
MAINT: aggregate covariance matrix info into an object
MAINT: do not silently reduce dimensionality, but allow reduction with a forcing flag
TST: more tests for singular covariance matrices
DOC: one eigh -> one call to eigh
DOC: add the allow_singular flag to more parts of the docs