--hight priority
--> See why a text_box doesn't display its content when the only parameter set 
  is the text

--> Add documentation
  calendar
  extended_calendar

--> use load_properties in all widgets
  line_graph.lua                  done
  triangular_progress_graph.lua   done 
  value_text_box.lua              done
  wlourf_circle_graph.lua         done
  progress_graph.lua              done
  net.lua                         done
  text_box.lua                    done
  calendar.lua                    done
  tagslist.lua
  popups.lua

--> use pango layout instead of cairo text functionnalities
  use helpers.draw_layout_and_baground
    line_graph.lua                done
    net.lua                       done
    progress_graph.lua            done
    triangular_progress_graph.lua done

--> create a grid module
  see how to deal sparse table (usage of the "-" doesn't seem very pro"
  check the fit method

--> text_box
  rename background_text_border to text_background_border
  or remove the property

simplify value_text_box
remove border for text background

-- clean calendar  almost done

clean helpers (some methods with too much parameters)
try to be consistent with the use of h_margin/v_margin names or h_padding/v_padding

--average priority
add more options in volume.lua (choose card, mpd address, mpd password ...)

Check all values in superproperties and in all files some of them doesn't match so user cannot modify some parameters:
check all for tagslist values
create a border value for tagslist (user set it with a color and a border of 1 px is displayed)
add superproperties values for task_warrior

Check in all files the usage of local values that have been set using user_value or superproperties value or nil
