Power metering

# What does it do?

The power metering module implements a simple IIR type running power meter. The damping factor of the IIR is selectable when the meter instance is created.

Note that the definition of dBOv is quite vague in most places - is it peak since wave, peak square wave, etc.? This code is based on the well defined wording in RFC3389:

"For example, in the case of a u-law system, the reference would be a square wave with values +/-8031, and this square wave represents 0dBov. This translates into 6.18dBm0".

# How does it work?