Implement WebGPIO polyfill for node backend

[dynamis]

Overview Description (Goal of this issue)

We want WebGPIO polyfill for node backend to make WebGPIO testable/usable on other devices. This make API consideration easy and fast. Also, many other devices including production embedded devices can share same code and ecosystem.

• [CHIRIMEN] - [current WebGPIO polyfill] - [browser applications]
• [node.js] - [gpio module] - [new WebGPIO polyfill] - [node applications]
• [node.js] - [gpio module] - [local gpio server] - (web socket?) - [another WebGPIO polyfill for Firefox] - [browser applications]

Action Itemc (Requirements to close this issue)

• [ ] select node version (6.x or later?)
• [ ] select node module for GPIO
  • https://www.npmjs.com/package/gpio ?
• [ ] implement WebGPIO polyfill on node
• [ ] implement WebGPIO polyfill on normal Firefox with local node backend

see also: #189

[naokisekiguchi]

I implemented a prototype of web gpio polyfill for node backend. https://github.com/naokisekiguchi/nodegpio

[dynamis]

create repo with new implementation: #195

[dynamis]

DONE by tadfmac: https://github.com/chirimen-oh/chirimen-raspi3