rename config_apply_color -> config_apply_style

add support for custom protocol proxies

add save_excursion and restore_excursion

allow changing the colors/attributes of the tabline

allow changing the attributes `attr' now follows the same rule as `fg' and `bg', with the three airity variant. Attributes by themselves are a comma-separated list of keywords, each one representing a ncurses attribute.

use term default color by default for every line type

allow customizing left and right padding + use_default_colors

allow changing the background color of the body window

rework color management: introduce the trailing props now, instead of prefix and line style, I'm adding the trailing style too. This changed the configuration syntax too.

first scratch for colour support!

kill empty line

add enable-colors (variable) currently unused, will help later when adding colour support

kill ui_notify and export {v,}message

move all cmd_* functions in their own file this detangles definitely the commands from the ui. Various variables and struct from ui.c needed to be exported, aside from that, no functional changes.

optimize redraw_window don't redraw the page if no scrolling happened. There's still need to ``force'' the redraw sometimes, like after a resize or after toggling olivetti-mode, so add a buffer->force_redraw flag for it.