Playing about with viewport setup
Add debug flag to dirty box draw
Added some more viewport functions
Added start of new function
Found cause of viewport issue. Added invalidate_sprite function.
Merge pull request #556 from duncanspumpkin/fix_viewports

Fix viewports
fix string format, peep real names not popping arguments
Fix another viewport issue by removing new function call it can be fixed at a later date. Change viewport address name to make it more obvious how to use it.
Remove redundant comment
Merge pull request #557 from duncanspumpkin/fix_view

Fix the other viewport issue
start implementing viewport_interaction_get_item_left