keep cursor on screen when pressing 'down'

Dependencies

• [2] Y6FTGOHJ simpler
• [3] PR4KIAZD first stab at equally hacky cursor down support
• [4] JY4VK7L2 rename
• [5] DLQMM265 scroll past first page
• [6] OTIBCAUJ love2d scaffold
• [7] XNFTJHC4 split keyboard handling between Text and Drawing
• [8] AVQ5MC5D finish uppercasing all globals
• [9] UWNHC4AA redo y computations
• [10] 537TQ2QN some more logging
• [11] 7IKRRESB longer names for indices in long loops
• [12] XX7G2FFJ intermingle freehand line drawings with text
• [13] H2DPLWMV snapshot: wrapping long lines at word boundaries
• [*] BULPIBEG beginnings of a module for the text editor

Change contents

• replacement in text.lua at line 6
  [5.2]→[4.1:31](∅→∅)
  − local Debug_new_render = true
  [5.2]

  [5.1567]
  + local Debug_new_render = false
• replacement in text.lua at line 126
  [5.627]→[4.311:337](∅→∅)
  − Debug_new_render = true
  [5.627]

  [5.627]
  + --? Debug_new_render = true
• edit in text.lua at line 289
  [3.789]

  [3.789]
  + print(Cursor_line, Cursor_pos, Screen_bottom_line)
• edit in text.lua at line 306
  [3.1620]

  [3.1620]
  + Screen_top_line = Cursor_line
• replacement in main.lua at line 114
  [5.44]→[2.3:43](∅→∅)
  − if y > Screen_height then break end
  [5.44]

  [5.546]
  + if y + math.floor(15*Zoom) > Screen_height then break end