v0.3.1

First of all, sorry about 9 commits in a single pull request, but at the beginning, I was not thinking to make the PR but at the end I've changed my mind.

The changes

• mgcrea@a0a1dac mgcrea@1c89d51 add attribute pull-to-refresh-config, with a test included (should solve the issue I've created mgcrea#18)
• mgcrea@061d6e2 add new demo with files hosted on github (before doing this I was struggling with a way of easy test it in different devices)
• mgcrea@f3085f2 mgcrea@94ab429 mgcrea@512b207 make it work and animate the "pull to refresh" using the JavaScript event. Native style momentum with overflow-scroll is not mandatory anymore (this may solve mgcrea#9)
• mgcrea@311da53 change a little bit the readme file, I hope this improves the documentation (should help mgcrea#12). Also added tested devices (mgcrea#9 also working on android mgcrea#4)
• mgcrea@574ee94 add optional dependency $translate (I need it in my App)
• mgcrea@129badb mgcrea@129badb make the tests pass

I didn't extend much with the tests, because I think this stuff is hard to test, and I didn't want to expend much time.