Fixes for methods using an old interface to _post

Couple of methods were calling _post with a raw hash of args instead of a hash ref, I assume this is an old interface to _post.

Methods are:
- create_invoice
- post_invoice
- post_invoiceitem

Also some whitespace trimming from my judicious editor

Some tests in live.t were broken also, I'll create a different issue for those and look at fixing them when I get a chance.