Speed up loading of 24/32-bit wav files.

[prayerie]

Reads the entire file into memory then does the byte skipping using memcpy, resulting in faster loading times for 24/32-bit samples.

Note: An additional temp buffer of audio data is required, so loading a large 24/32bit wav would be more likely to fail due to insufficient memory.

Note 2: audio_data_ is still up to 2x too large for 24/32-bit samples, however this PR doesn't address this :o)