Examples could be modernized

[marcoscaceres]

The examples do odd things in strange ways... like use .forEach to map to elements, etc.

They could be much improved.

[toyoshim]

keep this open for update in the future, and may work together with #174

[mjwilson-google]

See also #230

[mjwilson-google]

The examples are now in the explainer. Let's use this issue to track updating them.

[mjwilson-google]

There are still .forEach instances in the main body of the spec, so I will move this back to the CR milestone.

[mjwilson-google]

Specifically, in sections:
https://webaudio.github.io/web-midi-api/#MIDIInputMap
https://webaudio.github.io/web-midi-api/#MIDIOutputMap

And in the explainer here:
https://github.com/WebAudio/web-midi-api/blob/gh-pages/explainer.md#handling-midi-input

I'm not sure what other style issues we need to resolve.