Column: use std::shared_ptr's reset method instead
Column: ptr to each Column's parent Tab is now required
Handler: added another ctor and a move assign operator
Type_factory: changed the hash function to No_hash
added No_hash struct
List_dir: we're no longer caching directory contents
Tab: added Tab-wide cache for cursors
Handler: use implicit copy/move ctors/assign operators
Column: make move ctor noexcept
Tab: don't try to set the cursor in an empty List_dir
List_dir: don't calculate hash for an invalid cursor
make the namespace more apparent
dir.h: just moved get_cursor a few lines up
List_dir: removed a comment