This reverts commit 37423e4ff8.
Jeremy is right that we shouldn't remove this. The fact is that many
engines are depending on this middleware to be in the default stack.
This ties our hands and forces us to keep the middleware in the stack so
that engines will work. To be extremely clear, I think this is another
smell of "the rack stack" that we have in place. When manipulating
middleware, we should have meaningful names for places in the req / res
lifecycle **not** have engines depend on a particular constant be in a
particular place in the stack. This is a weakness of the API that we
have to figure out a way to address before removing the constant.
As far as timing attacks are concerned, we can reduce the granularity
such that it isn't useful information for hackers, but is still useful
for developers.
The runtime header is a potential target for timing attacks since it
returns the amount of time spent on the server (eliminating network
speed). Total time is also not accurate for streaming responses.
The middleware can be added back via:
```ruby
config.middleware.ues ::Rack::Runtime
```
Since all controller instances are required to have a request and
response object, RackDelegation is no longer needed (we always have to
delegate to the response)
* Fix a few remaining typos
* Wrap lines to 80 chars
* Fix the conversion from Textile to Markdown
* Update the part about `Rack::Cache` which isn't included anymore and
speak about Active Support's provided middleware
* Remove references to out-of-date methods and middlewares (e.g.
respond_with) and update the list of modules and middlewares to match
the actual code-base.
* Remove the middleware's description and links to the Rack guide
