Refine DNS rule for bottleneck

[taoeffect]

For now we're solving #103 with a slightly imperfect solution of looking at first character of subdomain.

A "perfect" solution to the problem that @SGrondin said to put on TODO is the following:

keep track of how many subdomains are being queried on that domain

then throttle each domain by the number of subdomains that have been queried. For example, citizenswebforum.com had like at least 50 subdomains iterated over in short period, then throttle everything going to citizenswebforum.com

(obviously treat all subdomain levels as a single subdomain, i.e. asdf.www should logically be treated as one subdomain, not two)

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