Add support for Array.find and/or Array.indexWhere

[Adam Wyłuda]

Find first element fulfilling given predicate. If no value is found then it will return either empty/null value of data class or empty Option proposed in #100.

[Adam Wyłuda]

Alternatively we could have Array.indexWhere which returns index of the found element or -1 in other case.

[Denys Shabalin]

👍