docs/phonemes.md: Add support for an elg (extra long) length feature.

docs/phonemes.md

@@ -336,6 +336,7 @@ the [length](#length) suprasegmentals are used instead.
 | `est`   | ◌̆      | extra short     |
 | `hlg`   | ◌ˑ     | half-long       |
 | `lng`   | ◌ː     | long            |
+| `elg`   | ◌ːː    | extra long      |
 
 ## References
 

src/libespeak-ng/phoneme.c

@@ -221,6 +221,7 @@ phoneme_add_feature(PHONEME_TAB *phoneme,
 	case hlg:
 		// Not supported by eSpeak.
 		break;
+	case elg: // FIXME: Should be longer than 'lng'.
 	case lng:
 		phoneme->phflags |= phLONG;
 		break;

src/libespeak-ng/phoneme.h

@@ -117,6 +117,7 @@ typedef enum {
 	est = FEATURE_T('e', 's', 't'),
 	hlg = FEATURE_T('h', 'l', 'g'),
 	lng = FEATURE_T('l', 'n', 'g'),
+	elg = FEATURE_T('e', 'l', 'g'),
 #	undef FEATURE_T
 } phoneme_feature_t;