ENH: min(max)imum_filter1d using the MINLIST algorithm, fixes #3898

This PR implements the minimum_filter1d and maximum_filter1d functions
using Richard Harter's implementation of the MINLIST algorithm. While
slower (~30%) than the MINLINE algorithm currently in place for random
inputs, its performance is consistent for all inputs, and is much
faster for long, ordered seqeunces.
Merge branch 'pr/3527' into master.

Review at https://github.com/scipy/scipy/pull/3527
BUG: Fix C90 compiler warnings in `NI_MinOrMaxFilter1D`

Variable declarations were preceded by code due to a rebase.
Merge pull request #4006 from jaimefrio/c90_warnings

BUG: Fix C90 compiler warnings in `NI_MinOrMaxFilter1D`