`visualize_spans` function + `manual` argument + docstrings

[pmbaumgartner]

Adds a visualize_spans function for using the span visualization in displaCy.

I made a few choices that may need justification:

• Even though spans_key is part of the options passed to displaCy, it feels critical enough to pass as an argument to visualize_spans rather than as a key/value in a dict to displacy_options - but we can obviously undo this.
• I didn't include the span viz in the "display everything" visualize function because none of the base models will have labeled spans in them, so it wouldn't display anything useful.
• Compared to visualize_ner:
  • I removed the manual argument because there's no such option for that with displaCy for spans
  • There's no label filtering/selection with spans, so all labels will be displayed for spans within a span_key. This removes the keys and labels args.

Extra:

• Also added a missing docstring for the show_table argument on visualize_ner (as well as visualize_spans)

Open questions:

• Is there a script to generate the nice readme.md documentation so we can include the new function?
• I'm not totally sure what needs to happen for a release, but I'm happy to help do whatever needs to be done!

[pmbaumgartner]

I've added a few more updates, so the name of this branch is a bit of misnomer now.

I've updated visualize_parser and visualize_spans to take an argument manual so that they can all take data in the format described here: https://spacy.io/usage/visualizers#manual-usage

I've also updated the docstrings to include this argument, as well as added the args to the docstrings for visualize_parser.

[pmbaumgartner]

Some smaller updates after testing out locally a bit more:

1️⃣ Added a very simple example app.

2️⃣ Added an exception catch if they have a version of spaCy before spans were supported in displaCy.

ValueError: 'visualize_spans' requires spacy>=3.3.0

3️⃣ Updated the README with a visualize_spans example and documentation.