Write example C program using Opus codec

Write example code for Linux using gcc compiler to encode and decode a sine wave. The result of this project will be used as a test driver for encoding/decoding various voice files. Parts of this example will be used in an embedded system transporting audio packets across a network.

Audio codec is the Open Source Opus codec. Documentation here: http://opus-codec.org

Project includes a single makefile which builds a single main.c and the Opus sources. Language is C.

main.c contains a global variable representing with the following source samples:
* 1kHz sine wave, sample at 16kHz at 16-bit depth
* 2kHz sine wave, sample at 16kHz at 16-bit depth
* 1kHz sine wave, sample at 48kHz at 16-bit depth
* 2kHz sine wave, sample at 48kHz at 16-bit depth

main() will perform the following:
(1) Opus encoder and decoder initialization
(2) Encode 5ms of a PCM sample (conditional compilation of one of the above samples)
(3) Decode encoded buffer; printf() decoded buffer
(4) Loop steps (2) and (3) until all 100ms of the buffer is processed

Verification of the results includes importing the data into Excel and plotting the reconstructed sine wave.

main.c contains summary of encoding parameters for tuning various parameters for high and low quality bitstreams.