Whole list of missing functions

[Shastel]

• [ ] attr()
• [x] blur()
• [x] brightness()
• [ ] calc()
• [ ] circle()
• [x] contrast()
• [ ] counter()
• [ ] counters()
• [ ] cubic-bezier()
• [ ] drop-shadow()
• [ ] ellipse()
• [x] grayscale()
• [x] hue-rotate()
• [ ] hwb()
• [ ] image()
• [ ] inset()
• [x] invert()
• [x] linear-gradient()
• [x] opacity()
• [x] perspective()
• [ ] polygon()
• [ ] radial-gradient()
• [x] repeating-linear-gradient()
• [ ] repeating-radial-gradient()
• [x] saturate()
• [x] sepia()
• [ ] url()