Add option dictionary to the AVURLAsset.

[jorgenhenrichsen]

Is your feature request related to a problem? Please describe.
Add a way to supply option key-values to the AVURLAsset by using init(url:options:).

Describe the solution or feature you would like
Should be able to supply these values to the AudioPlayer, which will pass it down to the AVPlayerWrapper that initializes the AVURLAsset.

Describe alternatives you've considered
A protocol that AudioItems can conform to in order to supply relevant options.

Additional context
A result of PR #64, that was adding auth headers to the asset by supplying headers in the option dictionary with the AVURLAssetHTTPHeaderFieldsKey key, but this is a private API. The feature described here offers a way for developers to use this at their own risk.