feat(main): export core types

core types can be reused externally

src/main.ts

@@ -4,10 +4,15 @@
 
 export {animationFrames} from './sources/AnimationFrames'
 export {filter} from './operators/Filter'
+export {forEach} from './lib/ForEach'
 export {fromArray} from './sources/FromArray'
 export {fromDOM} from './sources/FromDOM'
 export {fromPromise} from './sources/FromPromise'
 export {interval} from './sources/Interval'
+export {IObservable} from './types/core/IObservable'
+export {IObserver} from './types/core/IObserver'
+export {ISubscriberFunction} from './types/core/ISubscriberFunction'
+export {ISubscription} from './types/core/ISubscription'
 export {join} from './operators/Join'
 export {map} from './operators/Map'
 export {merge} from './operators/Merge'
@@ -19,6 +24,6 @@ export {sample} from './operators/Sample'
 export {scan} from './operators/Scan'
 export {skipRepeats} from './operators/SkipRepeats'
 export {slice} from './operators/Slice'
-export {forEach} from './lib/ForEach'
 export {switchLatest} from './operators/Switch'
 export {tap} from './operators/Tap'
+