Add initial support for Windows

- Support by TUN/TAP driver from OpenVPN
- Native Windows API without emulation
- Client up and down sample .bat scripts

Limitations:
    * Only support MinGW, not support Cygwin
      due to the TUN/TAP driver
    * Daemonize not working, can only run in
      the foreground
    * Scripts can only be written in batch file
      format, bash not supported
Add compiling guide for Windows
Fix detection of old MinGW toolchains
Fix compilation with old MinGW toolchains
Sample scripts support for older Windows
Merge branch 'linusyang-windows' into dev
update README
Catch window close event to run down script

Add warning when daemonize on windows
Merge pull request #21 from linusyang/windows

Run down script when closing app on Windows
Update README.md
Fix #20 winsock ECONNRESET problem
Suppress warnings of MinGW64 toolchain
Merge pull request #22 from linusyang/windows

Fix winsock ECONNRESET problem
bump