level plugin by thomas <thomas@apestaart.org>

this plugin signals:
  - running time since last EOS/start
  - channel
  - RMS level
  - peak level
  - decaying peak level
over the given interval.

This is useful for a VU meter display and for plotting out the signal graph.
The VU meter can either display RMS, or display immediate peak level and
have the falloff decaying peak level displayed as a line.

The interval for signal emission, ttl of decay peak, and falloff of decay peak
can all be set.

The element only takes unsigned data in; it could be extended to signed as
well, if separate fast chain functions are made that displaces the incoming
data to its midpoint (ie, 0,65535 should be mapped to -32768, 32767)

There are two demo apps, apps and plot.  apps will create some GTK sliders
to display the volume.  plot will output data readable by gnuplot.

Here is a sample plot script to plot output of the plot command that was
stored to plot.dat

set xlabel "Seconds"
set ylabel "dB"
set yrange [-60:0]
plot 'plot.dat' using 1:2 title 'L RMS' with lines, \
     'plot.dat' using 1:3 title 'L peak' with lines, \
     'plot.dat' using 1:4 title 'L decay' with lines

plot 'plot.dat' using 1:5 title 'R RMS' with lines, \
     'plot.dat' using 1:6 title 'R peak' with lines, \
     'plot.dat' using 1:7 title 'R decay' with lines