Continuation of infixowl update and coverage improvement

[ghost]

Summary of changes

Update of infixowl including a couple of minor run-time changes to avoid exceptions currently xfailing.

i) Continued improvement of coverage.
ii) Addressing of non-API flake8 issues of function and variable naming.

(Either as separate PRs or separate commits)

iii) Removal of non-functioning/unused code
iv) Change processing order in some methods to avoid raising Exceptions when arg is None
v) Further development of tests of infixowl functioning.
vi) Minor streamlining.
vii) Add documentation to illuminate noun and name ACE annotation usage

Checklist

• Checked that there aren't other open pull requests for the same change.
• Added tests for any changes that have a runtime impact.
• Checked that all tests and type checking passes.
• For changes that have a potential impact on users of this project:
  • Updated relevant documentation to avoid inaccuracies.
  • Considered adding additional documentation.
  • Considered adding an example in ./examples for new features.
  • Considered updating our changelog (CHANGELOG.md).
• Considered granting push permissions to the PR branch,
  so maintainers can fix minor issues and keep your PR up to date.

[coveralls]

Coverage increased (+0.1%) to 90.361% when pulling 559d7f5 on gjhiggins:infixowl-coverage-ii into 4f96f46 on RDFLib:master.

[aucampia]

Change looks good to me, will merge later today if there is no further feedback.