Miscellaneous code cleanups.

Including removal of old implicit args.
Performance fix for chain of filters using store_root().compute_at(output, y)
Bugfix for is_monotonic of a select
Bugfix for nested sliding windows.
Changed cascaded filter test to be simpler and to check the value.
Merge remote-tracking branch 'origin/master' into resize_example
Add different schedules and redefine '-s' option to switch between them.