support non-text lines in Text.to2

Dependencies

• [2] 3OKKTUT4 up and down arrow now moving by screen line where possible
• [3] H2DPLWMV snapshot: wrapping long lines at word boundaries
• [4] 2RXZ3PGO beginning of a new approach to scroll+wrap
• [*] BULPIBEG beginnings of a module for the text editor

Change contents

• replacement in text.lua at line 1740
  [3.7759]→[2.1162:1204](∅→∅)
  − assert(Lines[pos1.line].mode == 'text')
  [3.7759]

  [3.7759]
  + if Lines[pos1.line].mode == 'drawing' then

  + return {line=pos1.line, screen_line=1, screen_pos=1}

  + end