[Feature Request] Support for more color quantisation algorithms

[ashwani-rathee]

There is only 1 algorithm available and that too written specifically for RGBA format, It would be great to have the other algorithms like:

• Uniform quantisation
• K-means quantisation
• Median cut algorithm
• Octree quantisation
• K-d tree quantisation(Minimum variance partitioning)

I can help with last three fast ones