Windows support

I have no experience with C/C++, but after some googling I figured out how to build the native addon on windows. Basically:

1. in `binding.gyp` some warnings on windows are set to be ignored.
2. in `ph7_wrapper` we define `STDIN_FILENO` etc, and include `io.h` (Visual Studio replacement of `unistd.h`). That fixes [this](https://github.com/Deskshell-Core/node-ph7/blob/8920eed8a9b9b2d6adb67b5dfe2c144382ec62af/src/ph7_wrapper.cpp#L523) platform-specific line.

Other changes:

- Auto build on npm install (`node-gyp rebuild` as preinstall script). This is way easier to maintain than using separate binary packages per OS. Plus, it seems to be standard practice.
- Moved `lib/index.js` to `./index.js` (it's just one file) and directly require the compiled `ph7` addon
- Version bump (I also git tagged the previous version)