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

.coveragerc

@@ -4,6 +4,8 @@ source = parso
 [report]
 # Regexes for lines to exclude from consideration
 exclude_lines =
+    pragma: no cover
+
     # Don't complain about missing debug-only code:
     def __repr__