Added getColorQuantum to allow direct access to exact colors and tidied up quantum handling else. Small tidy up of method docs. Added tests for colors.
Normalised the methods for testing pixel similarity
isPixelSimilarQuantum - Normalised version 0-1
isPixelSimilar - Quantum version 0-QuantumRange
isSimilar - aka legacy method name aliased to isPixelSimilarQuantum
Merge pull request #43 from Danack/quantumTYpe

Quantum type is dependent on if ImageMagick was compiled as HDRI or not.