save each line's y coordinate, whether it's a drawing or not

Dependencies

• [2] VVXVV2D2 change data model; text can now have metadata
• [3] YHQC72JX slightly tweak boundary between concerns
• [4] JVRL5TWL store device-independent coordinates inside drawings
• [5] Z2CJVAPV lighter border for figures
• [6] XX7G2FFJ intermingle freehand line drawings with text
• [7] K6HMLFLZ color close to drawing
• [*] OTIBCAUJ love2d scaffold

Change contents

• edit in main.lua at line 92
  [3.72]

  [2.265]
  + line.y = y
• edit in main.lua at line 111
  [3.47]→[3.709:726](∅→∅),[3.709]→[3.709:726](∅→∅)
  − line.y = y