Fix names of functions that convert strings to addrs

Now let's have "lookup" indicate that there can be a hostname
resolution, and "parse" indicate that there wasn't.  Previously, we
had one "lookup" function that did resolution; four "parse" functions,
half of which did resolution; and a "from_str()" function that didn't
do resolution.  That's confusing and error-prone!

The code changes in this commit are exactly the result of this perl
script, run under "perl -p -i.bak" :

  s/tor_addr_port_parse/tor_addr_port_lookup/g;
  s/parse_addr_port(?=[^_])/addr_port_lookup/g;
  s/tor_addr_from_str/tor_addr_parse/g;

This patch leaves aton and pton alone: their naming convention and
behavior is is determined by the sockets API.

More renaming may be needed.