Insert a simple entry into the list of warnings filters (at the front).
A simple filter matches all modules and messages.
'action' -- one of "error", "ignore", "always", "all", "default", "module",
or "once"
'category' -- a class that the warning must be a subclass of
'lineno' -- an integer line number, 0 matches all warnings
'append' -- if true, append to the list of filters