v0.2.0

• Add CachedSyncIterable and CachedAsyncIterable.

  CachedIterable is now an abstarct base class. The sync version now
  lives in the CachedSyncIterable sublass, while the async one in
  CachedAsyncIterable.

• Add CachedAsyncIterable[Symbol.iterator]. (#1)

  The [Symbol.iterator] method returns a synchronous iterator over the
  elements cached by the CachedAsyncIterable instance.

• Add the static from(iterable) method. (#3)

  The static method from() may be used to create new instances from other
  iterables (which is the same as using the constructor) or to re-use
  existing ones. When an existing instance of a CachedIterable subclass
  is passed, from() simply returns it, preserving its cached state.