provide new line-distance property for built-in fonts

include/gint/display.h

@@ -291,8 +291,12 @@ typedef struct
 
 	/* Character spacing (usually 1) */
 	uint8_t char_spacing;
+	/* Distance between the y positions for two consecutive lines. This is
+	   an informative metric for text wrapping tools, not used by dtext()
+	   and other standard functions that always write a single line. */
+	uint8_t line_distance;
 
-    uint :24;
+	uint :16;
 
 	struct {
 		/* Unicode point of first character in block */

src/fxconv-metadata.txt

@@ -5,6 +5,7 @@ font5x7.png:
   grid.size: 5x7
   grid.padding: 1
   grid.border: 0
+  line-distance: 8
 
 font8x9.png:
   name: gint_font8x9
@@ -15,3 +16,4 @@ font8x9.png:
   grid.border: 0
   proportional: true
   height: 9
+  line-distance: 14