Add get_all_samples() method to AudioDecoder

[NicolasHug]

The most common decoding pattern for audio will be to decode an entire stream at once. Right now, the main way to do this is to call decoder.get_samples_played_in_range() which is a awkward:

• it's a long name
• we're not relying on the range feature

This PR introduces the decoder.get_all_samples() method which is a more natural alias, hopefully providing a better UX for the most common usage.

[scotts]

Can we add a brief comment explaining that the defaults for get_samples_played_in_range() do what we want, and that this method is a way of advertising that to folks?

[NicolasHug]

Absolutely, do you want it as a comment in the code or in the docstring?