Update spec regarding explicit strategy
Add RoundRobinWithTimeoutsStrategy

Currently considered a work-in-progress as I the
code really needs a cleanup. But hey, the specs
are passing. Yay!
Make RoundRobinStrategy thread safe

Which also includes RoundRobinWithTimeoutsStrategy
as it inherits from RoundRobinStrategy.
Rename @index to @current in RoundRobinStrategy
Refactor round-robin strategy specs
Rename RoundRobinWithTimeoutsStrategy

RetryableRoundRobinStrategy makes a bit more sense
but the name is still ridiculously long. Oh well.
Merge branch 'round-robin-with-timeouts'