Figure.histogram: Let parameter 'extreme' support Pythonic arguments

[seisman]

This PR migrates histogram's -L option to the new alias system and add support for Pythonic arguments.

The GMT CLI syntax is -Ll|h|b (https://docs.generic-mapping-tools.org/6.7/histogram.html#l), in which l|h|b are shorthands for low/high/both respectively. The table below summarize the current choices of parameter/argument names in GMT/PyGMT/GMT.jl:

	Parameter Name	Arguments
GMT option	-L	l/h/b
GMT long-option	extreme or out_range	low/first, high/last, both
PyGMT	extreme	first, last, both
GMT.jl	out_range	first, last, both

• GMT.jl: https://www.generic-mapping-tools.org/GMTjl_doc/documentation/modules/histogram.html).
• GMT: https://github.com/GenericMappingTools/gmt/blob/3604ba84e15e11e6977c4042a4af277506c9c51d/src/longopt/pshistogram_inc.h#L51

Personablly, I feel first/last are more readable and intuitive than low/high. So, this PR uses first/last, which is also consistent with GMT.jl.

One thing that still differs between GMT.jl and PyGMT is the parameter name. GMT.jl uses out_range, while PyGMT uses extreme. I feel out_range is more understandable. If we decide to use out_range, then we need to deprecate extreme to out_range in a few releases.