[tor-relays] Exitmap module to count CloudFlare CAPTCHAs

[Philipp Winter]

I wrote an exitmap module [0] that can tell us how many exit relays see
a CloudFlare CAPTCHA when connecting to a given site.

First, I ran the module for coreos.com because it uses CloudFlare, but
the owner configured it to whitelist Tor.  Indeed, only one out of 864
exit relays saw a CAPTCHA:
<https://atlas.torproject.org/#details/7DD29A65C370B86B5BE706EA3B1417745714C8AF>

Next, I ran the module for cloudflare.com, which does not seem to
whitelist Tor.  638 (75%) exit relays saw a CAPTCHA and 211 (25%)
didn't.

[0] <https://gitweb.torproject.org/user/phw/exitmap.git/tree/src/modules/cloudflared.py>

Cheers,
Philipp