Return result from thunk

Modified thunk function to return result. This enables use of implementations that return streams or promises for instance [redis-scanstreams](https://github.com/brycebaril/redis-scanstreams).

Also generated new commands for redis 2.8.x

Example:
```javascript

var redis = require('redis-scanstreams')(require('redis')),  // Extend redis to include a streaming scan implementation
     client = require('co-redis')(redis.createClient()),
     co = require('co');

co(function* () {
  // Get all keys using keys command
  yield client.keys('*');

  // Get all keys using scan
  yield buffer(client.scan({match: '*'})());  // Return stream
})();

function buffer(s) {
  return function(done) {
    var data = '';
    
    s.on('data', function(chunk) { return data+=chunk; });
    s.on('end', function() { return done(data); });
  };
}
```