Various cleanups

[anntzer]

Three independent cleanup commits:

• in axisartist: Mostly just unwrapping long lists of arguments and other expressions into a single line where possible.
• in contour: Shorten contour._make_paths_from_contour_generator.
• in dviread: Move most one-liner opcode parsers into lambdas with the behavior specified by comments, which seems clearer than spreading them out into proper functions with plenty of intervening blank space.

PR summary

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines

[ksunden]

Just some comment clean ups

[ksunden]

Suggested change

	# slen1: Read (delta + 1) bytes as an unsigned number.
	ulen1=lambda dvi, delta: dvi._arg(delta + 1, signed=False),
	# slen1: Read (delta + 1) bytes as an unsigned number if less than 4 bytes,
	# ulen1: Read (delta + 1) bytes as an unsigned number.
	ulen1=lambda dvi, delta: dvi._arg(delta + 1, signed=False),
	# olen1: Read (delta + 1) bytes as an unsigned number if less than 4 bytes,

[anntzer]

oops, fixed.