Add advanced usage section to docs about pysox

[Page-David]

If I am right, I do not think stats should be added into advanced usage, this is just get some basic information of a audio file.

[rabitt]

@Page-David I'd like stat and stats to be part of the "advanced usage" not because what they do is particularly complex, but because the methods behave differently than the rest of the Transformer methods. The "normal" Transformer methods like fade or silence are audio effects that applied when build is called. stat, however, doesn't affect the processing chain and instead simply returns information.

[Page-David]

I feel it likes to cause some misunderstanding as transform.stat looks like file_info.stat.

And doc List of frequency (Hz), amplitdue pairs. in transform.stats:

amplitdue->amplitude?

[rabitt]

I feel it likes to cause some misunderstanding as transform.stat looks like file_info.stat.

Yes good point. I've opened #46 to address this.

And doc List of frequency (Hz), amplitdue pairs. in transform.stats

yep there's a typo