Scintilla v5.5.7 officially requires at least GCC v9, but if it's
only the charconv header that's required from newer releases, v8.1
will probably do as well. We assume so until proven wrong.

* They have a newer version in pkgsrc, but it's not even available
  as a binary package on the arm6.
* Has some glitches, e.g. does accept the ASCII 27 in tutorial.ms,
  but it's probably not worth to work around.

* It requires a forced refresh on startup (even though that should be the
  default). Otherwise, it wouldn't print the info line correctly.
* Redirect stdin and pass it to newterm() to fix key queuing.
  Probably necessary for supporting ncurses on NetBSD as well.
* Avoid doupdate() if screen is too small: fixes crashes for very
  small windows.
* Updated Scintilla: There were some implicit typing assumptions,
  that are broken by this platform.

* PDCurses is practically used only for Windows builds, which only I build presumably,
  so it should be okay to bump the version.
* Older PDCurses versions had serious problems like not detecting BUTTONX_RELEASED events.
  This was worked around and is fixed now.
  Even the Wincon version behaves like ncurses now with regard to mouse events.
* We no longer have to support processing BUTTONX_CLICKED events.
  On the downside the mouse mask had to be adapted.
* See also https://github.com/Bill-Gray/PDCursesMod/issues/330
* We also no longer have to call resize_term(0,0).

* After installation, SciTECO will therefore start into a more userfriendly mode
  even if the user does not create a custom ~/.teco_ini.
  It is hoped that this will scare away less of new users, who
  are not willing to read through all of the documentation.
  Still, users are warned in the absence of ~/.teco_ini.
  This warning however, might not be immediately visible, especially
  not when running gsciteco without an attached console.
  (This will change once I redo the UI and allow a number of messages
  to be queued in the message area.)
* Theoretically, you could also just extend fallback.teco_ini from ~/.teco_ini,
  but that would require installing it into $SCITECOPATH.
* Since the fallback profile will now be munged automatically
  on a wide range of systems, we set up xclip only when detecting X11
  ($DISPLAY is non-empty).
  E.g. when running under Wayland or the Linux console, you still won't
  get the clipboard registers, which is probably better than having the
  clipboard operations fail once you try to use them.
* xclip is now "suggested" on Debian/Ubuntu.
  Unfortunately we cannot pull it in only in the presence of X11.

* You no longer have to copy contrib/scintilla, contrib/scinterm and contrib/lexilla
  manually to the build directory.
* It turns out, that Scintilla/Lexilla was supporting this since 2016.
  Scintilla allows pointing to a source directory (srdir) and Lexilla to a binary directory (DIR_O).
* For Scinterm I opened a pull request in order to add srcdir/basedir variables:
  https://github.com/orbitalquark/scinterm/pull/21
* `make distcheck` is therefore now also fixed.
* The FreeBSD package is now allowed to build out of source.
  I haven't tested it yet.
* See also https://github.com/ScintillaOrg/lexilla/issues/266

* it appears to behave similar to Mac OS with regard to recursions

* actually everything is updated to their current HEADs but the aforementioned versions are close.
* Scintilla uses threads now, so we added checks for pthread.
  To be on the safe side, we imported AX_PTHREAD from the Autoconf archives.
  The flags are kept out of the ordinary build system, though and used only for compiling Scintilla
  and for linking.
  SciTECO may also use threads, but via Glib.
* Scinterm removed SCI_COLOR_PAIR(), so we re-added it to src/interface-curses/interface.c.
* There is an Asciidoc lexer now.
* The <Ix$> interruption bug (see TODO) is not fixed by this upgrade.
  Perhaps the Mac OS version runs better now. Feedback is needed (refs #12).