implemented the <^A> command for printing arbitrary strings

* Greatly improved usability as a scripting language.
* The command is in DEC TECO, but in contrast to DEC TECO, we also
  support string building constructs in ^A.
* Required some refactoring: As we want it to write everything verbatim
  to stdout, the per-interface method is now teco_interface_msg_literal()
  and it has to deal with unprintable characters.
  When displaying in the UI, we use teco_curses_format_str() and TecoGtkLabel
  functions/widgets to deal with possible control codes.
* Numbers printed with `=` have to be written with a trailing linefeed,
  which would also be visible as a reverse "LF" in the UI.
  Not sure whether this is acceptable - the alternative would be to strip
  the strings before displaying them.
* Messages written to stdout are also auto-flushed at the moment.
  In the future we might want to put flushing under control of the language.
  Perhaps :^A could inhibit the flushing.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/qreg.h b/src/qreg.h
index 27a3653..2b970aa 100644
--- a/src/qreg.h
+++ b/src/qreg.h
@@ -45,6 +45,8 @@ extern teco_view_t *teco_qreg_view;
  * teco_qreg_set_integer_t set_integer;
  * ...
  * teco_qreg_set_integer(qreg, 23, error);
+ *
+ * But this probably won't work. Perhaps use the X-macro pattern.
  */
 typedef const struct {
 	gboolean (*set_integer)(teco_qreg_t *qreg, teco_int_t value, GError **error);