Changed flatMap methods to take same kind of Stream as the receiver.

Signed-off-by: Timo Kinnunen <timo.kinnunen@gmail.com>
Whitespace change.

Signed-off-by: Timo Kinnunen <timo.kinnunen@gmail.com>
Updated readme.

Signed-off-by: Timo Kinnunen <timo.kinnunen@gmail.com>