feature: support windows OS testing.

[wilhelmliao]

I patch a bit for supporting windows OS run testing.

• use dos command START /B, nginx.exe -s stop, TASKKILL, and wmic to manipulate processes.
• use String::Escape to encode file path text. Due to the windows path separator \ will be treat as nginx escape character.
• no nginx user directive on windows OS testing.
• patch non-blocking socket handling on windows OS.

  use POSIX::WSAEWOULDBLOCK signal