Finish #10
Tweak to use this method in Violet.Streaming
Introduce Violet.UserStream

+ add userstream.js
+ add userstream.js to makefile
+ use Violet.UserStream in init.js
Merge branch 'feature/issue#15' into develop
Introduce FilterStream (#11)

+ add filterstream.js
+ add filterstream.js to makefile

to use it, read `test/js/test_filterstream.js` and `https://dev.twitter.com/docs/api/1.1/post/statuses/filter`