New GNU Radio dependency

[Ron Economos]

For those building GNU Radio master branch from source, there is a new 
dependency that was introduced today with commit 
https://github.com/gnuradio/gnuradio/commit/18f64ba685cfc2533e2d7726aa43c524b007d97b.

On Ubuntu/Debian, it's:

sudo apt-get install libsndfile1-dev

This adds new capabilities to the WAV source and sink blocks. Specifically:

1) WAV files can now be unsigned 8-bit, 16-bit, 24-bit, 32-bit, float or 
double.

2) FLAC format is supported.

3) Ogg Vorbis format is supported.

4) 64-bit WAV files (files greater than 2 GB items in length) are supported.

Ron