improve explanation for buttons

Dependencies

• [2] OAHNWDYG .
• [3] ZNLTRNNK highlight another global
• [4] XX7G2FFJ intermingle freehand line drawings with text

Change contents

• replacement in button.lua at line 1
  [3.2058]→[2.108:141](∅→∅)
  − -- simple immediate-mode buttons
  [3.2058]

  [2.141]
  + -- Simple immediate-mode buttons with (currently) just an onpress1 handler for

  + -- the left button.

  + -- If the handler returns true, it'll prevent any further processing of the

  + -- event.