knockout.projections: Created typings and tests

Created a typings file for [knockout-projections](https://github.com/stevesanderson/knockout-projections) which has just been open sourced:  http://blog.stevensanderson.com/2013/12/03/knockout-projections-a-plugin-for-efficient-observable-array-transformations/

Even though the name of the library is "knockout-projections" I have called the typings "knockout.projections" to follow the existing standard being used for knockout related typings in DefinitelyTyped.  I hope that's correct?