Support M4B Audio Files

M4B audio files are just renamed m4a files. The different extension causes them to be automatically treated as audiobooks by players.

I've checked by modifying a copy of this module, support is as easy as adding the extension to the audio files whitelist on line three here:

https://github.com/stax76/Get-MediaInfo/blob/57e1e57d6d8f9048200b718dc2f36c1fa25d8e6e/Get-MediaInfo.psm1#L3