* impl the cursor_moved event
* re-impl line_changed as an extension of sig_mov (cursor_moved)
* add function to clear the last-row cache
*  move last-row clearing into sig_mov to avoid an extra kvm() call
* fix attribute error ..
* call sig_mov `on_selection_modified` and `on_activated` ..
* call sig_mod `on_modified`
* add lint stubs
* init lint.py