(8 Jul 2020, @ankostis): Sphinx AutoDocumenter; fix plot sfx-nodes

• FIX/FEAT(SPHINXEXT): so far, :func:.operation-annotated module functions were
  excluded from generated sites. Until the installed autodoc function-documenter
  was instructed how to render the wrapped function in place of the wrapping
  FnOp:

  • fix(fnop, pipeline): wrapped function attributes are conveyed to wrapping FnOp.

• FIX(plot): sideffect templates were left broken by recent privatization
  of modifier fields; add x2 Jinja-filters encapsulating the access to these fields.

• fix(op): fully fake callables by attaching a __qualname__ property on operations;
  also teach :func:.func_name() not to choke if __qualname__ missing.