Support for Preferences.jl #535

There are several arguments, mainly in color definitions and conversions.
On the other hand, satisfying all preferences is unaffordable in this package. Perhaps that is the job of a color management system.

I think we can reflect preferences on the issues of default value which we already have specifically.

The possibilities are:

• Default whitepoint

  • Colors.jl/src/cie_data.jl

    Line 16 in f0a508b

    const WP_DEFAULT = WP_D65

• Default CMF (not very important, but affects the drawing of chromaticity diagrams.)

  • Colors.jl/src/colormatch.jl

    Line 38 in f0a508b

    return colormatch(CIE1931_CMF, wavelen)

• Default max size of swatches

  • Colors.jl/src/display.jl

    Line 7 in f0a508b

    const default_max_swatches = 128 * 128

• Default diff. metric

  • Colors.jl/src/differences.jl

    Line 452 in f0a508b

    metric::DifferenceMetric=DE_2000()) = _colordiff(ai, bi, metric)

Again, do not try to satisfy all preferences. That will obviously spoil this package.