Implement .use() configuration

In response to https://github.com/tessel/camera-vc0706/issues/5, camera now configurable from .use() option, for one or both of compression and resolution.
```'ready'``` is not emitted until all configurations have completed without error.

An example using this new configuration:

```js
var tessel = require('tessel');
var Camera = require('camera-vc0706')

var camera = Camera.use(tessel.port['A'], {
    compression: 255, 
    resolution: 'vga'
  }, function(){console.log('Camera callback called')});

var notificationLED = tessel.led[3]; // Set up an LED to notify when we're taking a picture

// Wait for the camera module to say it's ready
camera.on('ready', function() {
  notificationLED.high();
  // Take the picture
  camera.takePicture(function(err, image) {
    if (err) {
      console.log('error taking image', err);
    } else {
      notificationLED.low();
      // Name the image
      var name = 'picture-' + Math.floor(Date.now()*1000) + '.jpg';
      // Save the image
      console.log('Picture saving as', name, '...');
      process.sendfile(name, image);
      console.log('done.');
      // Turn the camera off to end the script
      camera.disable();
    }
  });
});

camera.on('error', function(err) {
  console.error(err);
});
```