Add partial read option to read() function

[nikolai-kummer]

The user can now indicate in seconds the partial reading of wav files. This speeds up read times and reduces memory issues when trying to extract small sections from a large audio file.

[WarrenWeckesser]

@nikolai-kummer, thanks! I want to think a bit more about the API, and I might not get to it right away, but I want to let you know that I like the idea.