Add so-long library

* lisp/so-long.el: New library
* doc/emacs/trouble.texi: Briefly describe the problem and solution
* etc/NEWS: Include under "New Modes and Packages in Emacs 27.1"
1 job for scratch/so-long in 22 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #528
test

00:22:50

 
Name Stage Failure
failed
test Test
make[2]: *** [check-doit] Error 1
Makefile:309: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:279: recipe for target 'check' failed
make[1]: *** [check] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:955: recipe for target 'check' failed
make: *** [check] Error 2
ERROR: Job failed: exit code 1