IOxHelpers: research and provide additional operators

[getify]

RX operators to look more into adding in IOxHelpers:

• buffer(..) -- mostly the time based one, which is sorta zip-over-time
• takeUntil(..) -- waits on a value from another IOx to signal it should stop taking
• range(start,end) -- like seq(start,1) + take(end - start)
• forkJoin(..) -- like zip(..) but waits to emit only the last set of values
• concat(..) -- combinator (like merge(..) or zip(..), but goes in order)... would need a different name!
• pluck(..) -- like IOx's version of prop(..)
• find(..) -- like filterIn(..) + take(1)
• timeout(..)