A rough-and-pseudoready spectrograph using OpenGLES.
Uses the microphone on iOS and Mac OS X.

Most code is shared between the supported platforms, except for the EGL aspects and UI.

On OS X, you can install Soundflower (https://github.com/Cycling74/Soundflower) to reroute audio
into the app, particularly the system audio output. 
In the spectrogram app you need to pick Soundflower as the audio source using the Audio source menu.

*Outstanding issues:*
- Occasional overlap drawing produces bad column, need to simplify column sizing.
- Store/manipulate audio settings via a settings object.

*Missing features:*
- Use noise estimate to adjust the floor for the signal display.
- 3D mode