Fix aaline width and blend conflict

[ankith26]

• blend got removed in 2.4.0
• blend was re-added in 2.5.0 as a no-op
• added a width implementation in 2.5.2 but reverted it for that release only when it should have also been reverted for all upcoming releases.
• 2.5.3, 2.5.4 and 2.5.5 all use the initial width implementation. The problem here is that the width argument is coming in place of the depth argument so we are still breaking compat.
• just got the new width implementation in for 2.5.6.dev1. Still have the same issue as the previous three releases.

I saw 2 potential fixes for this situation:
fix 1: make width keyword only, put it after the blend arg, announce the API as new in 2.5.6 and pretend nothing happened in 2.5.[3-5]
fix 2: roll with whatever we have right now. This somehow works out because old code doing blend=1 or blend=True would now mean width=1 which is equivalent. We just need to add compat code that handles width <= 0 like width=1. We can then advertise that the "width argument replaces the blend argument" and old code doesn't break too bad.

[damusss]

Makes sense to me

[MyreMylar]

OK, the small internal API change makes sense to me. Should handle old code successfully without encouraging it and move us more smoothly into the new era of wider aalines.

It runs fine locally as well. Approved.