font: add delta symbol

Font5x7.c

@@ -91,21 +91,21 @@ const uint8_t x5x7_bits [] =
   /* Character (0x04):
      bbw=5, bbh=7, bbx=0, bby=-1, width=5
      +----------------+
-     |**              |
-     |*               |
-     |**              |
-     |* **            |
      |   *            |
      |  **            |
-     |  *             |
+     | * *            |
+     | * *            |
+     |*  *            |
+     |****            |
+     |                |
      +----------------+ */
-  0xc0,
+  0x10,
-  0x80,
-  0xc0,
-  0xb0,
-  0x20,
   0x30,
-  0x20,
+  0x50,
+  0x50,
+  0x90,
+  0xF0,
+  0x00,
 
   /* Character (0x05):
      bbw=5, bbh=7, bbx=0, bby=-1, width=5