Linux port

[randomgen]

The code builds and runs on Linux (Ubuntu 14.04 LTS), but the generated signal does not activate the Scentee diffuser.

Related commits:

• [x] 32c4a5983508c9dfe3a380958ddbcd3d9db4b597 Support Linux build
• [x] a65020569ce0e3eaf5b800cfe3bde916fe4dd727 Set output stream parameter to default low latency
• [x] 171fab3d193f9bbd3bf77eed2f2f518d08195124 Copy signal data to audio stream with 'memcpy'
• [x] Fix audio signal

[randomgen]

I have improved the audio signal generated with PortAudio and ALSA on Linux, but problems remain. I tried most solutions described in the documentation.

Low latency issues seem common with this software combination:

Of particular importance is PaAlsa_EnableRealtimeScheduling, which allows ALSA to run at a high priority to prevent ordinary processes on the system from preempting audio playback. Without this, low latency audio playback will be irregular and will contain frequent drop-outs.

Yes, I tried the ALSA extensions and to adjust the process priority with nice.

• http://portaudio.com/docs/v19-doxydocs/compile_linux.html
• https://www.assembla.com/spaces/portaudio/wiki/Tips_ClickingNoises
• https://www.assembla.com/wiki/show/portaudio/BufferingLatencyAndTimingImplementationGuidelines
• http://www.portaudio.com/docs/latency.html