Several new image and vector operations added. Docs provided but not updated.

Specifically:

Conversions:
Image makeRGBA8 : Image 
Image makeL8 : Image 
Image makeGrayscale : Image // This one leaves alpha if present.

Per-pixel transformations:
Image histogram : Vector
Image equalizeHistogram : self
Image linearContrast : self
Image componentPlain : Int -> self
Image bitPlain : Int -> self
Binarization:
Image thresholdByGradient : self
Image thresholdByHistogram : self
Image thresholdByOtsu : self

Local filters:
Image filterLinear : Int -> Int -> Vector -> Image
Special predefined forms:
Image filterUniformAverage : Int -> Int -> Image // Smoothing
Image filterGauss : Double -> Image // Smoothing
Image filterSobel : Int -> Image // Edge detection
Image filterKirsch : Int -> Image // Edge detection
Image filterNonlinearGradients : Image // Edge detection
Image filterUnsharpMask :: Int -> Image // Improves sharpness
Image filterMin : Int -> Int -> Image
Image filterMax : Int -> Int -> Image
Image filterMedian : Int -> Int -> Image  // Noise removal
Image filterWeightedMedian : Int -> Int -> Vector -> Image // Noise removal

Vector power operations:
Vector **= : ( Number | Vector ) -> self
Vector ** : ( Number | Vector ) -> self