DEP Deprecate steps plot argument in favor of matplotlib drawstyle

[drewejohnson]

Initially brought up in #432 for the HomogUniv class. As we start forwarding more plot options to the underlying matplotlib plot functions (#417, #423, #422 and friends) there may be a point where we want to rely on users passing drawstyle=<option> rather than our own logic for the step argument.

Some examples

serpent-tools/serpentTools/objects/containers.py

Line 411 in 67dc469

drawstyle = 'steps-post' if steps else None

serpent-tools/serpentTools/detectors.py

Lines 561 to 566 in 67dc469

	if steps:
	if 'drawstyle' in kwargs:
	debug('Defaulting to drawstyle specified in kwargs as {}'
	.format(kwargs['drawstyle']))
	else:
	kwargs['drawstyle'] = 'steps-post'

serpent-tools/serpentTools/objects/xsdata.py

Line 363 in 67dc469

kwargs.setdefault("drawstyle", "steps")

serpent-tools/serpentTools/parsers/sensitivity.py

Lines 408 to 409 in 67dc469

	ax.errorbar(energies, yVals, yErrs, label=label,
	drawstyle='steps-post')

Roadmap

I propose that by 0.10.0 we support passing steps and drawstyle for the methods that currently support steps. Methods like the sensitivity plotter can have a default drawstyle using kwargs.setdefault("drawstyle", ...).

Instances where both are passed should raise a DeprecationWarning by 0.10.0. Following 0.11.0 we should no longer support the steps argument, instead falling back to the matplotlib drawstyle argument.

Instances where we currently allow steps and additional kwargs should raise a pending deprecation warning by 0.9.4

Extras

Some care should be taken for the spectrum plot and other cases where we perform a line plot with some uncertainties. Here we wish to draw the errorbars in the middle of the bin (#428)