Add TypeScript definitions for store (fixes #1207)

store.d.ts

@@ -0,0 +1,23 @@
+interface Options {
+	immutable: boolean;
+}
+
+interface ObserveOptions {
+	defer: boolean;
+	init: boolean;
+}
+
+interface Cancellable {
+	cancel: () => void;
+}
+
+export declare class Store<State> {
+	constructor(state: State, options?: Options);
+
+	public compute(key: string, dependencies: string[]): void;
+	public get(): State;
+	public get<T>(key: string): T;
+	public observe<T>(key: string, callback: (value: T) => any, options?: ObserveOptions): Cancellable;
+	public onchange(callback: (state: State) => any): Cancellable;
+	public set(state: State);
+}