I believe this is all we need to implement throttling for all pages; this is currently limiting to 50 requests per second, per ip. (The result of the 'do' block is which cache key the request gets logged under, so for IP 127.0.0.1, they'll call something like 

`
Rack::Attack.cache['127.0.0.1'].to_i += 1
raise TooManyRequestsError if Rack::Attack.cache['127.0.0.1'] > 50
`

Might do to have another chat about how we want to customize this further; the 50 requests / ip / second number seems well out of normal browsing range, but it is arbitrary.

Seems to work for casual testing (if the rate limit is exceeded, the browser shoots back a `HTTP 429: Too many requests` error, but I want to have some automated testing surrounding that; could use a little help with that @s01us  @robguthrie @jonlemmon?