v0.6.6

Release notes:

• [scramble] Implement random-move scrambles for 5x5x5.
• Add 6x6x6 and 7x7x7 scrambles.
• Add 3x3x3 BLD and 5x5x5 BLD scrambles.
• Add 3x3x3 FMC scrambles.
• [ffi] Declare input and output as const.