configurable error handler when running tests

Dependencies

• [2] ARYMNK52 merge bugfix: show test failures
• [3] Q7HDVBN7 keep some prints in the terminal for now
• [4] 5ZCQGZP5 save 2 more alternate formats for test failures
• [5] FCFJVYKY redundant check
• [6] AVTNUQYR basic test-enabled framework
• [7] KKMFQDR4 editing source code from within the app
• [8] 3QMTXKWN rename
• [9] 3QNOKBFM beginnings of a test harness
• [10] IMEJA43L snapshot
• [11] 7CLGG7J2 test: autosave after any shape
• [12] CZQ3NJ4N Merge text0
• [13] NR43TWCN make App.open_for_* look more like io.open
• [14] JNJ4R56X support running tests multiple times
• [15] 36Z442IV back to commit 8123959e52f without code editing
• [16] ORRSP7FV deduce test names on failures
• [17] AD34IX2Z couple more tests
• [18] JOPVPUSA editing source code from within the app
• [19] 2CTN2IEF Merge lines.love

Change contents

• replacement in app.lua at line 72
  [2.33]→[5.8444:8462](∅→∅),[5.2302]→[5.8444:8462](∅→∅)
  − App.run_tests()
  [2.33]

  [5.1829]
  + App.run_tests(record_error_with_heuristic_location)
• replacement in app.lua at line 422
  [5.7396]→[5.7396:7421](∅→∅)
  − function App.run_tests()
  [5.7396]

  [3.18]
  + function App.run_tests(record_error_fn)
• replacement in app.lua at line 436
  [5.47]→[4.18:106](∅→∅)
  − xpcall(_G[name], function(err) record_error_with_heuristic_location(name, err) end)
  [5.47]

  [5.7548]
  + xpcall(_G[name], function(err) record_error_fn(name, err) end)