mix colors for hybrid recoding strategies

• define scripts/color.nu to manipulate RGB colors, especially mix two colors together
• compute the color of hybrid recoding strategies as a weighted sum of the two simple recoding strategies involved, e.g. if the strategy is "10% of the time recode 2 shards and 90% of the time recode 3", then the color of that curve will be 10% the color of the simple strategy recoding 2 shards and 90% the color of the other simple strategy recoding 3 shards
• make the hybrid curves transparent and dashed

example