Adaptor configs are too opaque

[nstott]

There's no way to query adaptors for their configuration options.
Adaptors take very specific flags in their config and we need to expose them to any commands.
My current thoughts is that the adaptor package should have a config registry, just as it has a registry of constructors.
Each config struct can then document itself via reflection tags, something like

type WhateverConfig struct {
    Uri string `json:"uri" transporter:"the uri to use to connect"`
}

this will address some of the concerns raised in #12

[jipperinbham]

Fixed via #22