Add <<Invoke>> bindings to button, listbox and menu, for consistancy with ttk.
Add documentation for <<EnteredChild>>, <<Invoke>>, <<Increment>> and <<Decrement>>
[Bug 3608074]: Add <<Invoke>> bindings to Button's, Listbox and Menu.
Document <<Invoke>>, <<ThemeChanged>>, <<EnteredChild>> (ttk_pandedwindow only) and <<Increment/Decrement>> (ttk_spinbox only)