Performance issues

[rporrasluc]

Hello, I spotted some performance issues in the middleware that can be really easily addressed. I am adding improvements as PRs, so I would really appreciate if they can be merged if they are ok. Any code change or improvement is welcome.

Thanks.

[rporrasluc]

First PR is #42, just avoiding blacklist and/or whitelist checks once it is already known that the page should not be prerendered.

[rporrasluc]

Second PR is #44. Please have a look to the PR description, I am specially concerned in so many calls to String#downcase method for any user agent that is not a bot (users for which the performance is really important).

[borisrorsvort]

@thoop Any chances you will be able to address those issues at some point ?

[rporrasluc]

Hello @borisrorsvort, I do not think such performance will be anyhow fixed by what I am suggesting. prerender middleware is usually slow because it needs to connect to prerender server, prerender server to get your web rendered and then give it back to the middleware.