[IMP] observer: add set and delete static functions

This rev. add a 'set' and 'delete' static functions to the Observer.
They allow to set or delete (only for objects) properties on
observed objects or arrays.

With this, the 'set' functions in Store and Component are no longer
necessary, so they have been removed.

Closes #138

src/store.ts

@@ -21,7 +21,7 @@ import { Observer } from "./observer";
 // Store Definition
 //------------------------------------------------------------------------------
 
-type Mutation = ({ state, commit, set, getters }, payload: any) => void;
+type Mutation = ({ state, commit, getters }, payload: any) => void;
 type Action = ({ commit, state, dispatch, env, getters }, payload: any) => void;
 type Getter = ({ state, getters }, payload) => any;
 
@@ -46,7 +46,6 @@ export class Store extends EventBus {
   debug: boolean;
   env: any;
   observer: Observer;
-  set: any;
   getters: { [name: string]: (payload?) => any };
 
   constructor(config: StoreConfig, options: StoreOption = {}) {
@@ -65,7 +64,6 @@ export class Store extends EventBus {
     if (this.debug) {
       this.history.push({ state: this.state });
     }
-    this.set = this.observer.set.bind(this.observer);
 
     for (let entry of Object.entries(config.getters || {})) {
       const name: string = entry[0];
@@ -110,7 +108,6 @@ export class Store extends EventBus {
       {
         commit: this.commit.bind(this),
         state: this.state,
-        set: this.set,
         getters: this.getters
       },
       payload