Add longoptions support for makecpt.

[rbdavis]

Description of proposed changes

Note: longoption strings copied wherever possible from existing and already
reviewed strings used in grd2cpt for very similar options. Also copied -T
'log2,log10,inverse,number' modifier strings from already reviewed gmtmath.

Python differences:

Changed -A transparency (conflicts with common options -t
transparency) to alpha.

Changed -H output to savecpt.

Julia differences:

Removed -A transparency alias (conflicts with common options -t
transparency).

Used wrap for -W wrapping directive (w) instead of as an alias
for the main longoption string.

Fixes #

Reminders

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