Add privoxy-blocklist

Privoxy is a very good filtering proxy, but it is useless without a configuration file.

`privoxy-blocklist` is a script that converts Adblock filters into the privoxy format.

Unlike the various ad blocking browser extensions, written in JavaScript, which are slow and use lots of RAM, Privoxy is written in C and is memory efficient, using about 20-30 MiB.

If configured system-wide, all applications will benefit from ad blocking.