Fixed a black hole state problem in AEBlockScheduler

Many thanks to AndreasHerbig for diagnosis and solution.
Fixed a podspec issue

Closes #64
Updated TPCircularBuffer

- Don't modify mDataByteSize buffer values on return from TPCircularBufferDequeueBufferListFrames
- Addressed a few warnings when building for 64-bit
Use float version of log10 in level meter calculation to avoid overflow issue

Closes #65
Thanks to rlopezdiez
Further tweaks to level metering
Make sure all AudioUnits continue rendering during screen lock.
Merge pull request #67 from milkllc/master

Make sure all AudioUnits continue rendering during screen lock.
Fixed an AEMixerBuffer issue with multiple dequeues in one time slice; increased max sources
Fixed bug calculating NSTimeInterval to timeStamps that are in the past

Time difference is calculated from two uint64_t (unsigned) values. To get correct results when the first value is less than the second value, we have to cast the result to an int64_t (signed) value.
Merge pull request #71 from manide/master

Fixed bug calculating NSTimeInterval to timeStamps that are in the past
AEFloatConverter: Make sourceFormat settable
Audiobus SDK 2.0 changes
Additional Audiobus 2.0 tweak
Fixed an Audiobus feedback issue with AEPlaythroughChannel
Support stereo when connected to IAA
Remove updateInputDeviceStatus from public header, instead update automatically on IAA connection change.
Added mixer channel count check to prevent -10877 errors.
Merge pull request #76 from psobot/psobot/10877-fix

Added mixer channel count check to prevent -10877 errors.
Merge pull request #74 from lijon/IAA_stereo_fix

IAA stereo fix
Fixed group converterNode resource leak.