Add the ability to modify request options

Adds a chaining method to a parent prototype, basically allows to modify request options if needed.

*Usage example:*
```javascript
var db = require('couchdb-api').srv('http://hostname:port').db(myDatabase);

db.ddoc(myKey).view(myView).setRequestOptions({
       timeout: 3 * 1000
}).query({
        limit: 1
}, function(err, data) {
        // do something
});
```