#42 - Debit object missing appears_on_statement_as field (but Hold has it and shouldn't)

The changes I've made ensure that Hold.appears_on_statement_as and Hold.description get propagated to Debit when Hold.capture() (either version) is invoked.

This probably isn't a good long-term solution, since (see #42) technically appears_on_statement_as isn't a field on hold on the server side.  That should probably be changed to an optional arg to capture(), and slapped on the capture payload at that point.

But anyway, at least it works now, if you do this:

hold.appears_on_statement_as = "whatever";
Debit debit = hold.capture();

...and debit.appears_on_statement_as (which was missing before entirely) is now set to "whatever".