* In principle --stdin and --stdout could have been done in pure TECO code using the
  <^T> command.
  Having built-in command-line arguments however has several advantages:
  * Significantly faster than reading byte-wise with ^T.
  * Performs EOL normalization unless specifying --8bit of course.
  * Significantly shortens command-lines.
    `sciteco -qio` and `sciteco -qi` can be real replacements for sed and awk.
* You can even place SciTECO into the middle of a pipeline while editing
  interactively:
  foo | sciteco -qio --no-profile | bar
  Unfortunately, this will not currently work when munging the profile
  as command-line parameters are also transmitted via the unnamed buffer.
  This should be changed to use special Q-registers (FIXME).
* --quiet can help to improve the test suite (TODO).
  Should probably be the default in TE_CHECK().
* --stdin and --stdout allow to simplify many SciTECO scripts, avoiding
  temporary files, especially for womenpage generation (TODO).
* For processing potentially infinite streams, you will still have to
  read using ^T.

* This command exists in Video TECO.
  In Video TECO it also supports reading multiple files with a glob pattern -- we do not support that
  as I am not convinced of its usefulness.
* teco_view_load() has been extended, so it can read into dot without
  discarding the existing document.

* this works by embedding the SciTECO parser and driving it always (exclusively)
  in parse-only mode.
* A new teco_state_t::style determines the Scintilla style for any character
  accepted in the given state.
* Therefore, the SciTECO lexer is always 100% exact and corresponds to the current
  SciTECO grammer - it does not have to be maintained separately.
  There are a few exceptions and tweaks, though.
* The contents of curly-brace escapes (`@^Uq{...}`) are rendered as ordinary
  code using a separate parser instance.
  This can be disabled with the lexer.sciteco.macrodef property.
  Unfortunately, SciTECO does not currently allow setting lexer properties (FIXME).
* Labels and comments are currently styled the same.
  This could change in the future once we introduce real comments.
* Lexers are usually implemented in C++, but I did not want to draw in C++.
  Especially not since we'd have to include parser.h and other SciTECO headers,
  that really do not want to keep C++-compatible.
  Instead, the lexer is implemented "in the container".
  @ES/SCI_SETILEXER/sciteco/ is internally translated to SCI_SETILEXER(NULL)
  and we get Scintilla notifications when styling the view becomes necessary.
  This is then centrally forwarded to the teco_lexer_style() which
  uses the ordinary teco_view_ssm() API for styling.
* Once the command line becomes a Scintilla view even on Curses,
  we can enabled syntax highlighting of the command line macro.

* This is trickier than it sounds because there isn't one single place to consult.
  It depends on the context.
  If the string argument relates to buffer contents - as in <I>, <S>, <FR> etc. -
  the buffer's encoding is consulted.
  If it goes into a register (EU), the register's encoding is consulted.
  Everything else (O, EN, EC, ES...) expects only Unicode codepoints.
* This is communicated through a new field teco_machine_stringbuilding_t::codepage
  which must be set in the states' initial callback.
* Seems overkill just for ^EUq, but it can be used for context-sensitive
  processing of all the other string building constructs as well.
* ^V and ^W cannot be supported for Unicode characters for the time being without an Unicode-aware parser

* this required adding several Q-Register vtable methods
* it should still be investigated whether the repeated calling of
  SCI_ALLOCATELINECHARACTERINDEX causes any overhead.