Increase audio decimation and decrease filter steepness to reduce CPU utilization.
Disable RDS resets for the time being as they seem to cause deadlocks.
Change xlate_bandwidth and freq_offset from sliders to variables.
Make the RF gain adjustable.
Change frequency slider to North American channel spacing.
Switch to GNU Radio's MPSK receiver for RDS demodulation.

The previous demodulator was using the stereo pilot as a phase reference
for the RDS PSK demodulator, but this doesn't always work because some
stations (several in my area) do not seem to have their RDS modulator
locked to their stereo pilot.  GNU Radio's MPSK receiver block uses a
Costas loop to recover the PSK carrier and decodes these stations well.
Merge pull request #2 from argilo/master

Various improvements to the sample GRC flowgraph