Add Invoicing api calls
Add tests for invoicing
Add samples for invoicing
Pin modules to specific versions. Fixes #32
Merge branch 'invoicing'

Merge in invoicing branch
add release notes
Match the tag names
Update with invoicing release notes
Remove changelog for release_notes
Bump version
Add invoicing to README
Merge branch 'rel-0.8.0' into stable

Merge in release branch
Merge branch 'stable'

Merge in stable