Move source to "MarantzVolumeMonitor" folder

[tillig]

Original request - PR #1

In order for the Arduino IDE to work with the "download" option in GitHub the .ino and other source files need to be in a child folder named the same as the .ino - "MarantzVolumeMonitor." GitHub appends the version/commit hash to the folder in the zip so using the download option doesn't work out of the box without a manual folder rename step.

[tillig]

In solving this it's a priority to ensure that Visual Studio and Visual Micro still work with the final file layout since that's my primary IDE.

[tillig]

Pushed the update for this just now.