I've updated `asyncLazy` implementation to make it...

# coroutines

[elizarov]

I've updated asyncLazy implementation to make it actually lazy (thanks @groostav for noticing it) and added isInitialized. Now it has feature-parity with a regular `lazy`: https://gist.github.com/elizarov/f27400a55c1502aacc35b4a3b2f5c9af