Add font property

Adds the following function:
------------------------------
obs_properties_add_font

This function creates a 'font' property to allow selection of a system
font.  Implementation by the UI should treat the setting as an obs_data
sub-object with four sub-items:
 - face:   face name (string)
 - style:  style name (string)
 - size:   size (integer)
 - flags:  font flags (integer)

'flags' can be any combination of the following values:
 - OBS_FONT_BOLD
 - OBS_FONT_ITALIC
 - OBS_FONT_UNDERLINE
 - OBS_FONT_STRIKEOUT

libobs/obs-properties.c

@@ -227,6 +227,7 @@ static inline size_t get_property_size(enum obs_property_type type)
 	case OBS_PROPERTY_LIST:      return sizeof(struct list_data);
 	case OBS_PROPERTY_COLOR:     return 0;
 	case OBS_PROPERTY_BUTTON:    return sizeof(struct button_data);
+	case OBS_PROPERTY_FONT:      return 0;
 	}
 
 	return 0;
@@ -386,6 +387,13 @@ obs_property_t obs_properties_add_button(obs_properties_t props,
 	return p;
 }
 
+obs_property_t obs_properties_add_font(obs_properties_t props,
+		const char *name, const char *desc)
+{
+	if (!props || has_prop(props, name)) return NULL;
+	return new_prop(props, name, desc, OBS_PROPERTY_FONT);
+}
+
 static inline bool is_combo(struct obs_property *p)
 {
 	return p->type == OBS_PROPERTY_LIST;

libobs/obs-properties.h

@@ -34,6 +34,7 @@ enum obs_property_type {
 	OBS_PROPERTY_LIST,
 	OBS_PROPERTY_COLOR,
 	OBS_PROPERTY_BUTTON,
+	OBS_PROPERTY_FONT,
 };
 
 enum obs_combo_format {
@@ -60,6 +61,11 @@ enum obs_text_type {
 	OBS_TEXT_MULTILINE,
 };
 
+#define OBS_FONT_BOLD      (1<<0)
+#define OBS_FONT_ITALIC    (1<<1)
+#define OBS_FONT_UNDERLINE (1<<2)
+#define OBS_FONT_STRIKEOUT (1<<3)
+
 struct obs_properties;
 struct obs_property;
 typedef struct obs_properties *obs_properties_t;
@@ -142,6 +148,18 @@ EXPORT obs_property_t obs_properties_add_button(obs_properties_t props,
 		const char *name, const char *text,
 		obs_property_clicked_t callback);
 
+/**
+ * Adds a font selection property.
+ *
+ * A font is an obs_data sub-object which contains the following items:
+ *   face:   face name string
+ *   style:  style name string
+ *   size:   size integer
+ *   flags:  font flags integer (OBS_FONT_* defined above)
+ */
+EXPORT obs_property_t obs_properties_add_font(obs_properties_t props,
+		const char *name, const char *description);
+
 /* ------------------------------------------------------------------------- */
 
 /**