create new() objects before passing to _post()

[sherrardb]

in some methods we _post() passed arguments directly:

stripe-perl/lib/Net/Stripe.pm

Lines 481 to 492 in 646861d

	} elsif (defined($customer)) {
	my %args = (
	account_balance => $account_balance,
	card => $card,
	coupon => $coupon,
	default_card => $default_card,
	email => $email,
	metadata => $metadata,
	);
	return $self->_post("customers/" . $customer, \%args);
	}

but in doing so, we are unable to take advantage of any magic that happens during objectification:

stripe-perl/lib/Net/Stripe/Resource.pm

Lines 22 to 26 in 646861d

	for my $f (qw/card default_card/) {
	next unless $args{$f};
	next unless ref($args{$f}) eq 'HASH';
	$args{$f} = Net::Stripe::Card->new($args{$f});
	}

and therefore have to duplicate it in the method:

stripe-perl/lib/Net/Stripe.pm

Lines 475 to 477 in 646861d

	if (defined($card) && ref($card) eq 'HASH') {
	$card = Net::Stripe::Card->new($card);
	}

where feasible, i think that we should use a pattern similar to post_subscription():

stripe-perl/lib/Net/Stripe.pm

Lines 781 to 799 in 646861d

	if (ref($subscription) ne 'Net::Stripe::Subscription') {
	my %args = (plan => $plan,
	coupon => $coupon,
	trial_end => $trial_end,
	card => $card,
	prorate => $prorate,
	quantity => $quantity,
	application_fee_percent => $application_fee_percent);
	if (defined($subscription)) {
	$args{id} = $subscription;
	}
	$subscription = Net::Stripe::Subscription->new( %args );
	}
	if (defined($subscription->id)) {
	return $self->_post("customers/$customer/subscriptions/" . $subscription->id, $subscription);
	} else {
	return $self->_post("customers/$customer/subscriptions", $subscription);
	}