Resize thread pool and set TcpStream timeout

[sigaloid]

This fixes the trivial attack of slowloris'ing 10 threads and holding them open forever.

1. the thread count is dynamic (up to 400 threads in my example but that's not a hard limit and depends on use case; it also rescales back down based on demand)
2. the stream is killed after one second (also depends on use case)

Basically just proposing an idea that the thread pool be resized. :)

[xvxx]

Awesome, thank you!

[xvxx]

I had to revert this because I am getting random !! io:Error: Thread timeout (std::io::ErrorKind::WouldBlock) errors now when I run any of the examples or any Vial app. All I have to do is load a page and hit refresh a few times, and it will fail almost right away. Not sure what is happening. I bumped the timeout and removed it and still saw the same issue.