added #play_freq

Win32::Sound.play_freq will take a frequency, a duration in milliseconds, and a volume and play the tone to the main sound device.  Adding this function required the implementation of several winmm structs and waveOut functions.  The test suite was also updated to match.  The private stream function was written in a way which allows for exstendibility for future code and features, such as opening an arbitrary wav file to a stream with any number of buffers.