Added support for playing a node specifying a sample rate

This is the beginning of an implementation to fix #33. For now, I have just created a function that allows specifying a sample rate instead of having to instantiate a stream by hand (to be used with, e.g., array players that do not have any info on the sample rate). If there's nothing wrong with this approach, we could add a similar function specialized for `FilePlayer` nodes (in this case, we do not need a sample rate argument, as the information is included in the `AudioFile` type.