Updates #3616. Squashed commit of the following: commit 06a65c3fe754f8f849f5e1648cc3d94d564bfa16 Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Fri Sep 17 14:31:06 2021 +0300 filtering: imp docs commit 9b6788453622ee19b0b383833e734d25e03a4d55 Author: Ainar Garipov <A.Garipov@AdGuard.COM> Date: Fri Sep 17 14:22:56 2021 +0300 filtering: fix special values in legacy rewrites