Update microphone "sound" methods to use the word "event" instead

[microbit-carlos]

To avoid confusion with the new class "Sound" for the audio module.

• microphone.current_sound -> microphone.current_event
• microphone.is_sound -> microphone.is_event
• microphone.was_sound -> microphone.was_event
• microphone.get_sound -> microphone.get_event

[jaustin]

Similar to #20 we're assuming this for resources.

[dpgeorge]

Done in 0d1c10b37bc7de0f7efae9a9695f7a1587f856c2