this aims to solve (albeit only partially) the confusion between telescope' ``struct window'' and ncurses WINDOW. It also brings some more emacs-like nomenclature, which may be a good thing.

to do that, move empty_vlist to wrap.c and provide a similar function for struct line*s.

- commands now take a struct window* instead of a raw tab - the struct ui_state is gone - using a window for the minibuffer too helps avoid code duplication - it will let us having more than one window on a tab! :DD It doesn't seem to have broken anything...

now that we have a bounch of -Wxxx flags during compilation, let's fix everything.