delete inapplicable issues

Dependencies

• [2] MD3W5IRA new fork: rip out drawing support
• [3] IDGP4BJZ new known issue with drawings
• [4] MTIS2XTC affirm a priority
• [5] OJBGNAN6 slight reorg in Readme
• [6] 34TC5SYK record another known issue I don't know how to fix yet
• [7] MOAEVTKJ clean up a few more loose ends
• [8] VC2CU2GG faster paste
• [9] F4QQIBEH clarify what "large files" means
• [10] EV36VCVF another known issue
• [11] 73OCE2MC after much struggle, a brute-force undo
• [12] VJ77YABH more efficient undo/redo
• [13] A2TQYJ6J .
• [14] 242L3OQX bugfix: ensure Cursor_line is always on a text line
• [15] MLG2OGU7 things seem to feel snappier now
• [*] FS2ITYYH record a known issue

Change contents

• replacement in README.md at line 61
  [3.15]→[3.18:95](∅→∅),[3.95]→[2.12041:12110](∅→∅)
  − * Undo/redo may be sluggish in large files. Large files may grow sluggish in

  − other ways. Works well in all circumstances with files under 50KB.
  [3.15]

  [3.276]
  + * Undo/redo may be sluggish in editor windows containing large files. Large

  + files may grow sluggish in other ways.