Clients all in sync... when it works. Host isn't.

TODO
To fix host: get rid of separate host queue.
Investigate inconsistent startup bug.
Removed separate host queue, need to fix host sampling jitter.
Time sync works perfectly w/ 4 clients... for approx 6.5 minutes.

After ~6.5 minutes client readings get messed up -- variable overflow?
Haven't tested with more than 4.
Cleaned up old commented code/junk.
Interrupt-safety changes. Fixes queue position corruption.

Doesn't fix time synchronization.
Changed to interrupt timer instead of polling.

Doesn't work any better than last commit, unfortunately.
Somewhere the host is dropping readings or losing track of time.
Clients all stay in sync with each other (minus some jitter),
but host gradually offsets its own samples to output too soon.
FIXED SYNC PROBLEMS! About time.

Only works right for one device at the moment, need to track skew
for each client instead of just once.
Cleaned up code (removed old commented out parts, mostly).

Untested since I don't have access to RFDuino's right now, but it
compiles and there isn't any reason this should break.
Better comments/explanation of host code.
Alpha version of per-client skew correction... half works.
I don't even know. Host stops receiving messages.

Something to do with higher sampling rates.
GZLL crashing/getting overloaded?
Merge branch 'master' into queue_rewrite