do we need filters as a top-level plugin type?

[bttmly]

It seems like most filters are only relevant to specific mutators (e.g. the tweak-string mutator can know to avoid tweaking require("thing")) – is it necessary to have a top level filter plugin?

Since they are already supported and seem (potentially) useful probably won't remove them entirely, but all of the current filters seem like they should go into mutators.

NOTE: it may be that we want to change where filters get applied. There should probably be a way to stop recursive descent and move on if a node meets certain qualities.