Allow iterables, not just arrays, as child elements

[blzaugg]

This would allow mapping over any iterable (like Immutable.js) object, rather than having to convert those objects to arrays.

Code before:

{myList.map(
    // ...
).toArray()}

Code after:

{myList.map(
    // ...
)}

Pro:

• Faster code, as you don't have the overhead of converting to array.
• Less implementation code.

React added this feature in v0.13.0:
facebook/react@c07ea0b

From Lee Byron (no relation) on avoiding conversion:
https://twitter.com/leeb/status/746733697093668864?lang=en