Implement Draw-time Transparency Resolution

[viluon]

Render-time transparency resolution has its use cases, but draw-time transparency is a must-have feature. It avoids having to use a secondary transparent overlay buffer to use transparency features and thus has a potential to improve performance by miles.

• Branch buffer off to buffer-dtt
• Implement draw-time transparency resolution in drawing functions
• Implement non-resolving :render methods
• Make DTT available with buffer:import()

[viluon]

DTT is a debatable feature again. As buffer gets faster and faster (#16 and #15 will likely mean another major increase in performance), it's questionable whether the performance benefits of DTT will be worth the necessary management of a much larger code base. We'll have to profile this.

[viluon]

Draw-time transparency will be a part of Desktox. Final decision.