Adding additional support for payment methods.
Add line item helpers to bill line item model.
Alias TotalAmt methods to be consistent.
Merge pull request #183 from benzittlau/extend-payment-methods

Adding additional support for payment methods.
Merge pull request #184 from benzittlau/add-bill-line-item-helpers

Add line item helpers to bill line item model.
Merge pull request #185 from benzittlau/total_amount_consistency

Make the API for total amounts consistent
Implement delete for bill payments.
Add support for bill payment deletion.
Merge pull request #186 from benzittlau/add-bill-payment-deletion

Add bill payment deletion