refactor(Subscription): allow Subscription to add Subscription<any>

Allow the Subscription to add a child Subscription parameterized by <any>, not by <T>. There isn't a
clear reason why all child Subscriptions should be type <T>, and there are cases where we need to
have a <any> child.

src/Subscriber.ts

@@ -58,7 +58,7 @@ export class Subscriber<T> extends Subscription<T> implements Observer<T> {
     }
   }
 
-  add(sub: Subscription<T> | Function | void): void {
+  add(sub: Subscription<any> | Function | void): void {
     // route add to the shared Subscription if it exists
     const _subscription = this._subscription;
     if (_subscription) {
@@ -68,7 +68,7 @@ export class Subscriber<T> extends Subscription<T> implements Observer<T> {
     }
   }
 
-  remove(sub: Subscription<T>): void {
+  remove(sub: Subscription<any>): void {
     // route remove to the shared Subscription if it exists
     if (this._subscription) {
       this._subscription.remove(sub);

src/Subscription.ts

@@ -47,7 +47,7 @@ export class Subscription<T> {
     }
   }
 
-  add(subscription: Subscription<T>|Function|void): void {
+  add(subscription: Subscription<any>|Function|void): void {
     // return early if:
     //  1. the subscription is null
     //  2. we're attempting to add our this
@@ -58,7 +58,7 @@ export class Subscription<T> {
       return;
     }
 
-    let sub = (<Subscription<T>> subscription);
+    let sub = (<Subscription<any>> subscription);
 
     switch (typeof subscription) {
       case 'function':
@@ -78,7 +78,7 @@ export class Subscription<T> {
     }
   }
 
-  remove(subscription: Subscription<T>): void {
+  remove(subscription: Subscription<any>): void {
 
     // return early if:
     //  1. the subscription is null