Add support of partial classes. [Mixins](https://github.com/Microsoft/TypeScript/wiki/Mixins) is not the same, because it's run-time realization. Need compile realization, where partial classes will be combine into one before converting typescript to javascript. ``` javascript //FileA.ts partial class ClassA { constructor(public name: string) {} public sayHello(): string { return "hi!"; } } //FileB.ts partial class ClassA { public sayBye(): string { return "by!"; } } ``` will be: ``` javascript partial class ClassA { constructor(public name: string) {} public sayHello(): string { return "hi!"; } public sayBye(): string { return "by!"; } } ```