prismatic 0.2.0

• Added clr_alpha() function to specify transparency. (#9)
• Added labels argument to plot.colors() to show hexcode in plot. (#8)
• clr_rotate()'s argument degrees now default to 0.
• clr_mix()'s argument ratio now correctly takes varied lengths as the argument.
• added check_color_blindness() to allow quick visual color deficiency examination. (#11)