Moved generate invoice method to receive a dto instead 6 parameters
Story creating is now responsability of the DefaultStoryBuilder and not of InvoiceGenerator anymore
Moved footer text to a constant
All data and constants were moved to Data class which lives in dtos.py
Refactor functional test
Remove unused imports
Moved subtotal to metadata dto
Type of units is now responsability of strategy
Updated README
Merge pull request #4 from initios/feature/data

Moved generate invoice method to receive a dto instead 6 parameters