1.0 release (highlighting improvements, API stabilization)

[smjonas]

Currently, if you change the word tall into far (e.g. with :Norm ciwfar), you will get three separate highlights (two replacements and one deletion - if deletion edits are shown). This is confusing and not very useful.

Once this PR is completed, there will be a single substitution edit (or replacement edit, I am not 100% sure on the name yet) per word, removing edits if necessary.

This will also mark version 1.0 of this plugin which I can then finally release :tada:.

To Do:

• [x] fix skipped_start_cols being nil with wax for input string type
• [x] only remove whole word suffix / prefix in strip_common
• [x] fix b_start being nil with f"x on line " test
• [ ] improve readme (better demo + pitch, 1. show replacements and insertions with :Norm, then show deletions with :G command, link to Discussions page)

New features

• new edits provider improved_levenshtein
• added edits_provider option
• added should_substitute option

Breaking changes in this PR

• hl_groups.replacement has been renamed to hl_groups.change
• hl_groups will now be merged with the defaults. false must be used to disable highlighting for a particular highlight type.