This allows passing children to `StatelessComponent<P>` exactly like base components without the need to use React.Props<T> or extending the P interface with an explicit 'children' property:
# Before
````typescript
type FooProps = {
bar: number;
}
const Foo: React.SFC<FooProps> = props => (
<div>
{props.children} = {props.bar} // error TS2459: Type 'FooProps' has no property 'children' and no string index signature.
</div>
);
````
# After
````typescript
type FooProps = {
bar: number;
}
const Foo: React.SFC<FooProps> = props => (
<div>
{props.children} = {props.bar}
</div>
);
<Foo bar="42">6×9</Foo> // <div>6×9 = 42</div>
````
