Add test for monthly period generation around February and modify
generation method to pass.
Add test for end of month due date generation.
Add test for date generation with due date at beginning of month.
Add test for monthly due date generation where the due date is within
the month.
Add test cases for YEARLY due date generation and fix the generation
function so that they pass
Merge remote-tracking branch 'origin/master'

Conflicts:
	budget.py