cli: add support for multiple option occurence
cli: add support for multiple option occurence

By using the 'multiple' key in the command structure, the command class
can be instructed to allow multiple occurences of the same option. This
is well suited for entering things like tags or our new AVPs
(extra-attributes) of which there could be several ("multiple") for each
prefix.

plajjan/NIPAP,SoundGoof/NIPAP,plajjan/NIPAP,garberg/NIPAP,ettrig/NIPAP,bbaja42/NIPAP,SoundGoof/NIPAP,garberg/NIPAP,bbaja42/NIPAP,bbaja42/NIPAP,plajjan/NIPAP,fredsod/NIPAP,SoundGoof/NIPAP,plajjan/NIPAP,garberg/NIPAP,ettrig/NIPAP,bbaja42/NIPAP,fredsod/NIPAP,SoundGoof/NIPAP,ettrig/NIPAP,fredsod/NIPAP,fredsod/NIPAP,SpriteLink/NIPAP,fredsod/NIPAP,bbaja42/NIPAP,garberg/NIPAP,SpriteLink/NIPAP,SpriteLink/NIPAP,SoundGoof/NIPAP,bbaja42/NIPAP,plajjan/NIPAP,SpriteLink/NIPAP,plajjan/NIPAP,ettrig/NIPAP,garberg/NIPAP,fredsod/NIPAP,ettrig/NIPAP,SpriteLink/NIPAP,SoundGoof/NIPAP,SpriteLink/NIPAP,garberg/NIPAP,ettrig/NIPAP