Add vendor to memo
Fix invoice stub for show
Create invoices table
Use a join table for memos/pieces
Add invoice seeds
Serve live invoice data for index and show
Serve live vendor data
Serve live memo data and minor invoice fixes
Use yajl for json

This allows for pretty-printed json output in development mode
Serve live piece data
Mark some piece columns as non-null
Remove unnecessary comments
Add count to stones
Piece api updates and tests
Improvements for piece api/tests

Update isn't working yet
merge pieces