Standardize naming style and some other hanges

- All getters and setters including boolean queries use camelCase
i.e. getFrameCount(), setVol(), isActive()
- All methods use lowercase_with_underscores,
i.e. pa_callback(), setup_source()
- AschMixer has been made into a class to hide the vol and pan
instance variables and its mixing functions have been named as
mix() to prevent confusion with its constructors.
update .gitignore