prismatic 1.0.0

• All functions now accepts zero length input.
• Added contrast_ratio() function to calculate contrast ratios between colors. (#18)
• Added modify_hcl() function to modify individual HCL axes. (#20)

Breaking changes

• clr_rotate() now uses HCL instead of HSL as its color space for rotation. (#19)
• clr_lightness() and clr_darken() now uses HCL instead of HSL as its default color space. (#19)