Non-uniform quantization experiment

Non-uniform quantization experiment

This framework allows lower quantization bins to be shrunk down or
expanded to match closer the source distribution (assuming a generalized
gaussian-like central peaky model for the coefficients) in an
entropy-constrained sense. Specifically, the width of the bins 0-4 are
modified as a factor of the nominal quantization step size and from 5
onwards all bins become the same as the nominal quantization step size.
Further, different bin width profiles as well as reconstruction values
can be used based on the coefficient band as well as the quantization step
size divided into 5 ranges.

A small gain currently on derflr of about 0.16% is observed with the
same paraemters for all q values.
Optimizing the parameters based on qstep value is left as a TODO for now.

Results on derflr with all expts on is +6.08% (up from 5.88%).

Experiments are in progress to tune the parameters for different
coefficient bands and quantization step ranges.

Change-Id: I88429d8cb0777021bfbb689ef69b764eafb3a1de