Add: First pass at click in Preview window to sync with editor window.
Docs: Document the preview module.
      Begin writing about the preview sync feature.
      Clean code to follow docs.
      Include preview.py in the documentation tree top for now. Later, it
        should probably be included by its __init__.py.
Add: Approximate matching routines from CodeChat.
     First-pass integration into Enki's preview window.
     Build instructions for tre, a prerequisite for approximate matching.
Docs: Improve sync explanation.
Add: Code to move the cursor in the text pane.
Docs: Modernize and improve approx matching docs.
Refactor: Rename to ApproxMatch.
Docs: Rewrite, modernize style, and clarify.
Refactor: Change test name to match module refactor.
Fix: Make tests work with unittest and in the Enki test environment.
Add: TextToPreview sync code.
Fix: Try to maching method naming convention: a leading underscore indicates a
       private method.
Fix: No longer neet QtWebKit hook, since preview.py now explicitly imports it.
     Add hidden import of widgets.
Docs: Add a to-do list.
      Record helpful web references.
Fix: Select line, rather than surrounding characters, in text to web sync.
Fix: Prevent assertion when text to web find string is empty, causing the find to
       fail.
Fix: Run without preview sync if TRE can't be imported.
Add: Logging to show match results.
Fix: On web to code sync, use correct search text.
Add: Test of web-to-code sync.
Fix: Use simpler assertion now provided in base.py.
Docs: Include additional files in Sphinx build.
Docs: Put in unit-testing ideas. Update to-do list.