Potential performance wins

[k0nserv]

There are a few potential performance wins you can explore here I think.

1. Use a trie rather than a linear scan for the prefix matching.
2. You could allocate less in filter. For example, by directly building a Vec<u8> instead of a String. Currently there are two allocations, a Vec<&str> and String. With that approach you'd only have one and you could potentially allocate with too much capacity to prevent resizing the Vec.

EDIT: With the signature pub fn filter(block_list: &Vec<String>, buf: &mut [u8]) -> &mut [u8] and some index fiddlig you could probably entirely avoid allocations in filter.