gtest: support precise timing on iOS
made audioconvert compatible with ffmpeg 2.2.2
Added the possibility to dynamically set the folder paths for files used in tests (needed for mobile platforms like iOS)
essentia test: allow free-standing main() entry point for when the main() name is already taken (e.g. iOS apps)
Apple Instruments hot-spot "fix": multiply by inverse
Apple Instruments hot-spot "fix": use single-precision math functions