Changed customer to introduce some basic relationship logic.
updated
updated customer_repo_test to match invoice_repo_test closes #32
Updated item_test to have a setup method so it doesn't cause test problems in the future
updated low level class tests to have setup methods for making data used in tests to prevent possible future problems
merging 31 with current master
Merge pull request #37 from trayo/merge_31_master

Merge 31 master