Curses: added support for cool Unicode icons (refs #5)

* Practically requires one of the "Nerd Font" fonts,
  so it's disabled by default.
  Add 0,512ED to the profile to enable them.
* The new ED flag could be used to control Gtk icons as well,
  but they are left always-enabled for the time being.
  Is there any reason anybody would like to disable icons in Gtk?
* The list of icons has been adapted and extended from exa:
  https://github.com/ogham/exa/blob/master/src/output/icons.rs
* The icons are hardcoded as presorted lists,
  so we can binary search them.
  This could change in the future. If there is any demand,
  they could be made configurable via Q-Registers as well.

doc/sciteco.7.template

@@ -2304,6 +2304,12 @@ Scinterm manual, documenting the mapping of
 Scinterm manual
 .UE
 .TP
+Suitable terminal fonts for icon support in Curses (see
+.BR ED command).
+.UR https://www.nerdfonts.com/
+Nerd Fonts
+.UE
+.TP
 Gtk+ 3 documentation, containg details about
 its CSS support and syntax:
 .UR https://developer.gnome.org/gtk3/stable/GtkCssProvider.html

sample.teco_ini

@@ -59,6 +59,9 @@ EMQ[$SCITECOPATH]/fnkeys.tes
 ! Uncomment if XTerm allows clipboard operations !
 ! 0,256ED !
 
+! Uncomment to enable Unicode icons in the Curses UI !
+! 0,512ED !
+
 ! Uncomment to tweak the memory limit !
 ! 500*1000*1000,2EJ !
 

src/core-commands.c

@@ -2065,6 +2065,11 @@ teco_state_ecommand_close(teco_machine_main_t *ctx, GError **error)
  *     Should only be enabled if XTerm allows the
  *     \fIGetSelection\fP and \fISetSelection\fP window
  *     operations.
+ *   - 512: Enable/Disable Unicode icons in the Curses UI.
+ *     This requires a capable font, like the ones provided
+ *     by the \(lqNerd Fonts\(rq project.
+ *     Changes to this flag in interactive mode may not become
+ *     effective immediately.
  *
  * The features controlled thus are discribed in other sections
  * of this manual.

src/interface-curses/Makefile.am

@@ -6,4 +6,5 @@ AM_CFLAGS = -std=gnu11 -Wall -Wno-initializer-overrides -Wno-unused-value
 noinst_LTLIBRARIES = libsciteco-interface.la
 libsciteco_interface_la_SOURCES = interface.c \
                                   curses-utils.c curses-utils.h \
-                                  curses-info-popup.c curses-info-popup.h
+                                  curses-info-popup.c curses-info-popup.h \
+                                  curses-icons.c curses-icons.h