r32

Based on Gradation Curves 1.45.

Additions:

• 64-bit and cross-platform support.
• AviSynth+ filter.
• Increase maximum number of points from 16 to 32.
• VirtualDub: disable Smooth button when not in Pencil mode.

Fixes:

• Initialize RGB<->LAB LUTs just once.
• Preserve alpha channel.
• Fix segmentation fault when saving VirtualDub project.