ER: Normalisation flags made availabe

[brendan-pike]

I would like to request that more values for volume management be made available as flags for enc.py, Reading the volume section in http://www.mltframework.org/twiki/bin/view/MLT/Services I believe that the following would be helpful, gain, max_gain and limiter. Having access to these per file should enable a user to fine tune things much better.

It would also be nice if a user could create custom normalisation settings in veyepar.cfg for quick recall. For example:

[Normalization]
heavy=gain:5max_gain:20,limiter=15
medium=max_gain:10,limiter=11
light=max_gain:2,limiter=5

Which could then be set with something like ./enc.py --custom-normalization medium