Don't hardcode display support

[thijstriemstra]

The arguments in the example options parser should be dynamically populated. Basically every lib should advertise what display modes/interfaces are available.

[thijstriemstra]

This also requires some sort of API coming from luma.core I imagine. Any library or simple plugin system we can use here? I have some of these escpos printers and I'm thinking of creating luma.escpos just for fun, that basically provides an emulator that prints every frame directly to a thermal printer. So I'd create such a package and then luma.examples should somehow know (like django) that there's an escpos emulator available (or any other emulator/display) when a certain package is installed. Thoughts?

[rm-hull]

i guess the first place to start looking might be the inspect module or pyclbr possibly?

Alternatively recursively check and descend into list(pkgutil.walk_packages(luma.__path__)) importing packages as you go

[rm-hull]

Fixed in #18