i3bar: use Pango markup

Parse text within workspace buttons and the i3bar statusline as Pango
markup. This lets people specify things like font weight, text color,
background color, font size, and font family in the text of i3bar.

fixes #1468

libi3/string.c

@@ -20,6 +20,7 @@ struct _i3String {
     xcb_char2b_t *ucs2;
     size_t num_glyphs;
     size_t num_bytes;
+    bool is_markup;
 };
 
 /*
@@ -39,6 +40,19 @@ i3String *i3string_from_utf8(const char *from_utf8) {
     return str;
 }
 
+/*
+ * Build an i3String from an UTF-8 encoded string in Pango markup.
+ *
+ */
+i3String *i3string_from_markup(const char *from_markup) {
+    i3String *str = i3string_from_utf8(from_markup);
+
+    /* Set the markup flag */
+    str->is_markup = true;
+
+    return str;
+}
+
 /*
  * Build an i3String from an UTF-8 encoded string with fixed length.
  * To be used when no proper NUL-terminaison is available.
@@ -59,6 +73,20 @@ i3String *i3string_from_utf8_with_length(const char *from_utf8, size_t num_bytes
     return str;
 }
 
+/*
+ * Build an i3String from an UTF-8 encoded string in Pango markup with fixed
+ * length.
+ *
+ */
+i3String *i3string_from_markup_with_length(const char *from_markup, size_t num_bytes) {
+    i3String *str = i3string_from_utf8_with_length(from_markup, num_bytes);
+
+    /* set the markup flag */
+    str->is_markup = true;
+
+    return str;
+}
+
 /*
  * Build an i3String from an UCS-2 encoded string.
  * Returns the newly-allocated i3String.
@@ -133,6 +161,13 @@ size_t i3string_get_num_bytes(i3String *str) {
     return str->num_bytes;
 }
 
+/*
+ * Whether the given i3String is in Pango markup.
+ */
+bool i3string_is_markup(i3String *str) {
+    return str->is_markup;
+}
+
 /*
  * Returns the number of glyphs in an i3String.
  *