mbrola: add mb-es4 voice

Makefile.am

 	espeak-ng-data/mbrola_ph/en1_phtrans \
 	espeak-ng-data/mbrola_ph/es_phtrans \
 	espeak-ng-data/mbrola_ph/es3_phtrans \
+	espeak-ng-data/mbrola_ph/es4_phtrans \
 	espeak-ng-data/mbrola_ph/fr_phtrans \
 	espeak-ng-data/mbrola_ph/gr2_phtrans \
 	espeak-ng-data/mbrola_ph/grc-de6_phtrans \
 	mkdir -p espeak-ng-data/mbrola_ph
 	ESPEAK_DATA_PATH=$(PWD) src/espeak-ng --compile-mbrola=phsource/mbrola/es3
 
+espeak-ng-data/mbrola_ph/es4_phtrans: phsource/mbrola/es4 src/espeak-ng
+	mkdir -p espeak-ng-data/mbrola_ph
+	ESPEAK_DATA_PATH=$(PWD) src/espeak-ng --compile-mbrola=phsource/mbrola/es4
+
 espeak-ng-data/mbrola_ph/fr_phtrans: phsource/mbrola/fr src/espeak-ng
 	mkdir -p espeak-ng-data/mbrola_ph
 	ESPEAK_DATA_PATH=$(PWD) src/espeak-ng --compile-mbrola=phsource/mbrola/fr

docs/mbrola.md

 | `es1`        | Spanish              | male   | `mb-es1` | `mbrola-es1`   |
 | `es2`        | Spanish              | male   | `mb-es2` | `mbrola-es2`   |
 | `es3`        | Spanish              | female | `mb-es3` |                |
-| `es4`        | Spanish              | male   |          |                |
+| `es4`        | Spanish              | male   | `mb-es4` |                |
 | `fr1`        | French               | male   | `mb-fr1` | `mbrola-fr1`   |
 | `fr2`        | French               | female | `mb-fr2` |                |
 | `fr3`        | French               | male   | `mb-fr3` |                |

espeak-ng-data/voices/mb/mb-es4

+language es 4
+name spanish-mbrola-4
+gender male
+mbrola es4 es4_phtrans

phsource/mbrola/es4

+volume 15
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