Add NodeOrLeaf.dump() and NodeOrLeaf.search_ancestor() (#187)

- Add `NodeOrLeaf.dump()` to generate a readable and "round-trippable" dump for a parser tree
- `parso.tree.search_ancestor()` is deprecated, use `NodeOrLeaf.search_ancestor()` instead
- Set up children's parent in `BaseNode.__init__()`
- Add test for `search_ancestor`
- Various small type annotations improvements

.gitignore

@@ -11,3 +11,4 @@ parso.egg-info/
 /.pytest_cache
 test/fuzz-redo.pickle
 /venv/
+/htmlcov/