HalConfigurer objects should be individually queryable, validated, etc

[richteer]

This might go hand in hand with #107 .

If in #107 there is queryable table of expected config keys, and so on, they should also be validateable without need for a prompt.

Use case: config module where the syntax is something like !config irc.nickname = foobar, where "foobar" is ambigiously typed (and received as string).