Code generated uses flaot64 for price amounts

[sbrossie]

See https://github.com/killbill/kbcli/blob/master/kbmodel/invoice_item.go#L29

[hibrid]

@sbrossie Forgive my naiveness... what is wrong with float64? I suppose the precision level is more than overkill and I'm wondering if that is all there is to this issue?