Windows Support

### Changeset

Added libwinpty in deps/winpty. I've made some minor changes and committed them upstream, but these are not related to the library itself.

### Remarks

Only pty.fork() is supported.
Unit tests fails, could somebody care to investigate why?

### Demo
```
git clone https://github.com/chjj/tty.js.git
cd tty.js
npm install
cd node_modules
rd /s /q pty.js
git clone https://github.com/peters/pty.js.git
npm install
cd ../../
node bin/tty.js
```

And you shall have unicorns!