Some constants that affect editor behavior:
* `Margin_top`, `Margin_left`, `Margin_right` are integers in pixel units that
  affect where the editor is drawn on window (it always extends to bottom of
  window as needed)
* `Drawing_padding_top` and `Drawing_padding_bottom` affect spacing around
  drawings.

* Various color constants are represented as tables with r/g/b keys:
  * `Text_color`, `Cursor_color`, `Highlight_color` for drawing text.
  * `Stroke_color`, `Current_stroke_color` for line drawings.
  * `Icon_color` affects the color of the little mode icon on the top right of
    a drawing.
  * `Current_name_background_color` manages the color when naming points using
    `ctrl+n`.
  * `Focus_stroke_color` affects the color of a point or line when you hover
    over it.
  * `Help_color` and `Help_background_color` affect the color of online help
    within line drawings.