Meta::ZeroClickInfo: simplify supported attributes check.

Streamline to a single code path for checking key/value pairs.

The hash key look up will be faster than checking against every
element in the array from the function call each time.

On the other hand, even though I got here somehow, I can't actually see
where it will get run.
Meta::ZeroClickInfo: change supported attributes init and check.

We don't really care too much about the values we are setting.  I
considered setting all the values to `undef` which saves some
infinitesimal amount of space, but also confuses people.

Instead, make it easy to add an attribute as if it were a simple list,
while getting the benefits of a fast `exists` check for set membership.

Thanks to @nilnilnil for the suggestion.
Add ZCI handling of structured answers.

Simply place a perl data structure in structured_answer and everything
will proceed apace.
IsControllable: move in `caller` attribute from Spice.

In order to do some of the nice things with loading files on behalf of
the IA, we need to make this available across at least Goodies and
Spice.
Merge pull request #94 from mwmiller/structure

Structure