Store bound update method in constructor and use it as callback

[blikblum]

Currently each time update method is used as callback, it pass a new / different bound instance
The callback is not removed when unobserve is called and each time the same object is bound to a rivets view the callback count increases.

Another side effect is the memory leak, independent of the object be rebound to a view, because observer instance cannot be collected so the binding and the HTMLElement.

The issue can be see in examples as simple as http://s.codepen.io/blikblum/debug/BjYPgo
Just break at rivets.adapter['.'].unobserve, click in bind / unbind and see 'person' callbacks increase

[blikblum]

Just see #12 now. Basically the same, just with a different name

[stalniy]

@mikeric I believe a lot people would like to see this being merged!

[ydaniv]

Sorry for the noise, but a big +1!

[mikeric]

Hey guys, merging this in. Sorry for my lack of involvement over the past year. Glad to see there are many people interested in furthering the development of these projects.

@Duder-onomy, @Leeds-eBooks I've added you guys as contributors to this project as well, since their releases often need to be coordinated.