Packer (#172)

* introduce pako and add general packer interface

* add tests for packer

* use function API instead of class API for better tree shaking support

* refcatoring the rollup bundle config

typings/index.d.ts

@@ -2,5 +2,6 @@ import record from './record';
 import { Replayer } from './replay';
 import { mirror } from './utils';
 export { EventType, IncrementalSource, MouseInteractions, ReplayerEvents, } from './types';
+export { pack, unpack } from './packer';
 declare const addCustomEvent: <T>(tag: string, payload: T) => void;
 export { record, addCustomEvent, Replayer, mirror };