Switch to xcb-xkb and libxkbcommon

This removes our last dependency on Xlib! :)

(Okay, an Xlib dependency still comes in through other libraries that we
 link against, but it’s not us. Our code is simpler by this change and
 uses one less connection to X11.)

src/bindings.c

@@ -8,6 +8,8 @@
  */
 #include "all.h"
 
+#include <xkbcommon/xkbcommon.h>
+
 pid_t command_error_nagbar_pid = -1;
 
 /*
@@ -263,8 +265,8 @@ void translate_keysyms(void) {
             continue;
 
         /* We need to translate the symbol to a keycode */
-        keysym = XStringToKeysym(bind->symbol);
-        if (keysym == NoSymbol) {
+        keysym = xkb_keysym_from_name(bind->symbol, XKB_KEYSYM_NO_FLAGS);
+        if (keysym == XKB_KEY_NoSymbol) {
             ELOG("Could not translate string to key symbol: \"%s\"\n",
                  bind->symbol);
             continue;