enhanced tuning support, and a few bug fixes.

Hi, while trying out uSpeech and attempting to get reasonable results from my setup, I made a few enhancements that might be of interest to you.

The installation debug demo now keeps a history of phonemes and outputs them to help check word matches, and it supports switching between debug options.

I added a scale factor to compensate for low levels from the spark fun mems microphone I'm using, and added mic power threshold to remove more noise from the system.