timbr 0.3.0

• Fixed a bug where forests with grouped root nodes (e.g. those produced by summarise()) could error or behave incorrectly in downstream operations.
• children() now gives a clear tidyselect error when a forest's root nodes don't share a single node name, instead of an internal assertion failure.
• climb()'s .deep argument has been renamed to .recurse (.deep is now deprecated), and a recursion bug that could corrupt node bookkeeping when climbing multiple levels has been fixed (#9).
• leaves() now correctly returns forests where every node is both root and leaf (e.g. single-level trees), instead of erroring.
• map_forest() is now defunct and throws an error; use traverse() instead (it has been deprecated since timbr 0.2.2).
• relocate() is now implemented for forests, moving columns while preserving the tree structure.
• rows_patch() and rows_update() are now implemented for forests, with fixes to by-column matching and error messages (#20).
• select() for forests now always preserves the internal node column, so selecting feature columns no longer breaks the tree structure.