[WIP] Overhaul of internals

[natevw]

The primary concerns driving this:

• the original implementation did not have a great async story (some internal race condition bugs in certain cases)
• there are a few ugly explicit "wait for this event before using X" checkpoints, perhaps some can be eliminated now too
• it was hard to document the pipe options and address picking behavior, some clearer modes and perhaps even a bit more manual effort on part of user planned here (not much progress yet)
• more abstract hardware API for cleaner support of e.g. Tessel (and perhaps johnny-five)
• intend to deal with Arduino "reversed data" in this pass too
• and add an A–Z tutorial for the common case of talking between RF24 on Arduino and node-nrf on Raspberry Pi

TBD: cross-reference above narrative with open issues, add any other pain points that should be included in this pass.