* This could have been in ring.c, but in the future we may want to script
  the behavior in case recovery files are detected.
* The warnings are currently written as user messages, which looks
  ugly in interactive mode.
  Once n^A is supported, we can write them as regular warnings, though (FIXME).

* Go-to statement was broken since v2.5.0.
* see also b65c64a200dac8194dacc90ae2150b683f64cd8a

Usually, we should prefer the hardware cursor, but on
slow terminal emulators, you could see the cursor jumping across the screen.

* This allows for several customizations.
  * You can simply increase the visible command line history.
    For that you must also set SCI_SETWRAPMODE(SC_WRAP_CHAR).
    An example was added to fallback.teco_ini.
  * You could also set SCI_SETLINEENDTYPESALLOWED(SC_LINE_END_TYPE_DEFAULT)
    to see the structure of inserted text.
* Alternatively we could have introduced a new command like EP or FW
  and also overload it to replace the current ED&2048 (e.g. -EP and EP).
  In DEC TECO `W` comes closest to what 5EJ now does.

* M[lexer.set.cmdline] can be used to set up syntax highlighting on the command line
  (if desired).
* Color schemes with light-dark themes (solarized.tes) are now responsible
  to update the command line view as well.

* The unnamed buffer is also used for reading from --stdin, so you couldn't practically combine
  --stdin with passing command-line arguments to macros.
* The old approach of passing command-line arguments via lines in the
  unnamed buffer was flawed anyway as it wouldn't work with filenames containing LF.
  This is just a very ancient feature, written when there weren't even long Q-reg names in SciTECO.
* You can now e.g. pipe into SciTECO and edit what was read interactively, e.g. `dmesg | sciteco -i`.
  You can practically use SciTECO as a pager.
* htbl.tes is now a command-line filter (uses -qio).
* grosciteco.tes reads Troff intermediate code from stdin, so we no longer need
  "*.intermediate" temporary files.
* added a getopt.tes test case to the testsuite.
* This change unfortunately breaks most macros accepting command-line arguments,
  even if they used getopt.tes.
  It also requires updating ~/.teco_ini - see fallback.teco_ini.

* `[q]~` was broken and resulted in crashes since it reset the clipboard character to 0.
  In fact, if we don't want to break the `[a]b` idiom we cannot use the numeric cell
  of register `~`.
* Therefore we no longer use the numeric part of register `~`.
  Once the clipboard registers are initialized they completely replace
  any existing register with the same name that may have been
  set in the profile.
  So we still don't leak any memory.
  (But perhaps it would now be better to fail with an error
  if one of the clipboard registers already exist?)
* Instead, bit 10 (1024) of ED is now used to change the default
  clipboard to the primary selection.
  The alternative might have been an EJ flag or even a special register containing
  the name of the default clipboard register.
* partially reverses 8c6de6cc718debf44f6056a4c34c4fbb13bc5020

* It continues to default to 67 (C), which is the system clipboard.
  But you can now overwrite it e.g. by adding `^^PU~` to the profile.
* This fixes a minor memory leak:
  If you set one of the clipboard registers in the profile (initializing
  them as plain registers), the clipboard register had been leaked.
  The clipboard registers now replace any existing register,
  while at the same time preserving the numeric part.
* All remaining Q-Reg table insertions use a new function
  teco_qreg_table_insert_unique() which adds an assertion, so that
  we notice any future possible memory leaks.

* Improves DEC TECO-11 compatibility.
* <EM> is still supported as a synonym, but considered deprecated and is no longer documented.
  A warning is printed when invoked.
  It can be repurposed at any time in the future.
* `EI$` is not yet supported.
  I am unsure whether this makes any sense.