Add blacklist filter

[dsaxton]

$ cargo test

...

running 8 tests
test tests::test_deserialize_input_message ... ok
test tests::test_blacklist_accept ... ok
test tests::test_register_builtin_filters ... ok
test tests::test_blacklist_reject ... ok
test tests::test_load_config ... ok
test tests::test_run_filters_shadow_reject ... ok
test tests::test_run_filters_accept ... ok
test tests::test_whitelist_reject ... ok

test result: ok. 8 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

   Doc-tests noteguard

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

[jb55]

sorry I somehow missed this, will test!